The private key which your vanity address is derived from is like any other private key. It provides 128 bits of security.
A 24 word BIP39 seed phrase provides 256 bits of entropy.


They are different.
The term "passphrase" is usually used to refer to characters or words you use to extend your seed phrase. When you add a passphrase to your seed phrase, you generate a completely different wallet.
In bitcoin core, the passphrase is like a password which encrypts your wallet file.

Are you saying hacking electrum is easier than hacking Atmoic wallet, trust wallet, Exodus, etc?
If so, you are completely wrong. Electrum is open-source. The code has been reviewed by many people and no vulnerability has been found.
When it comes to a close source wallet like trust wallet, it's possible that there's a vulnerability which makes the attack easier for hackers.

In electrum, you can choose to not encrypt the wallet file and only encrypt your secrets. In this way, you can open your wallet, check your balance and transaction history without any need to enter a passworda and you will be asked for your password whenever you want to make a transaction.

To do so, you must uncheck "Encrypt wallet file" when choosing your password.

So, it's electrum wallet file and since you don't have the seed phrase, you must know the password to be able to spend fund from your wallet.
If the password is simple and you have some idea about that, you may be able to brute-force the password. If you haven't created the wallet yourself and you have purchased that, you have been scammed and I recommend you to not waste your time.

Asking the user to update the wallet with a fake version of electrum was possible in the versions older than 3.3.4.
If you are using the new versions, you are right. You should be safe.

In versions 3.3.3 and before that, there was a vulnerability which allowed servers to display any arbitrary message. Server could abuse this feature and display a message including a link to a fake website and ask the user to update the wallet through that website.

Wrong.
As already mentioned, the warning is related to the privacy and it's displayed by blockchair.com when there's only 1 output in the transaction. The warning has nothing to do with one's security and the amount of bitcoin that is transacted.


Blockchair.com displays that warning for any transaction that has only 1 output, even if the there are multiple inputs.

There is no way to do that. There's a big probability that they have paid the acceleration fee from a different address.
For accelerating a transaction using their paid service, ViaBTC gives you an address to make the payment and you can send the fee from any of your addresses.

Just with deleting your private key from your device, you make your paper wallet secure.
Most people generates their paper wallet incorrectly. For generating a paper wallet, you should use a safe tool on an airgapped device.


There is no coinjoin in electrum.


When you use a open-source wallet, you can review the code and know how exactly it's working.
For example, we are sure that there is no backdoor in electrum.

With using a change address, you can confuse blockchain analyzers to not know which of the receiving addresses is owned by the recipient and which of them is the change. That's why blockchair.com suggests having a change. But you don't really need to always do that and you are right. That's not accurate. If you make a transaction with only 1 output, it's more like sending the fund to yourself or making a deposit to an exchange.

You can surely improve your privacy in that way, but those addresses are still linked with each other somehow.

The warning mentioned by OP is displayed on blockchair.com when a transaction has exactly 1 output and it has nothing to do with the amount you send.
In the case your transaction has only 1 output, you will see that warning, even if you send only 1000 sat.

Blockchair.com suggests not sending the whole balance, so that the transaction has a change.

The point here is that you should check the address, whether you copy-paste it or you use a QR code. As mentioned by o_e_l_e_o, the risk is never zero.


No.
If you change the receiving address or any other data, the signature will become invalid and you have to sign the transaction again.


I remember Metamask used to display the first 4 and the last 4 characters.
I just pasted an ETH address in Metamask to see if it's still the same. It displayed the first 11 and the last 4 characters.

Yes. You can download the android version of bluewallet from their official website.


Atomic wallet?
It seems that you are unaware of what happened to Atomic wallet recently. Visit the topic created by Wind_FURY a few days ago.
A Non-Custodial wallet, Atomic Wallet, being compromised

Yes. You can spend unconfirmed outputs.
Just note that you can't get confirmation for the child as long as the parent hasn't been confirmed. If the fee rate used for the child is equal or greater than the parent, both transactions will be included in the same block.


Yes, you can see many of them in the blockchain.

The private key of address A was probably compromised and the thief stole the fund. That's all. It could be due to the device being compromised or using a fake wallet.  
Note that miners can include both parent and child in the same block and there is no problem with that.

The thief saw the receiving transaction to the address A and made a transaction to address B while the transaction to address A was still unconfirmed.
The fee paid for these transactions was high enough and a miner included both of them in the same block.

Note that there are two different coinbase wallets. One of them is non-custodial and gives you a seed phrase and the other one is custodial.
I guess OP is referring to the non-custodial coinbase wallet here. If that's the case, he/she should be able to spend the fund once the receiving transaction gets one confirmation. It's also possible to import the wallet to electrum and spend the fund even when the receiving transaction is still unconfirmed.

It may worth mentioning that even their non-custodial wallet should be avoided. It's close source and there is no way to know how the keys are generated.

I mentioned Trezor, because it's surely one of the most popular hardware wallets. I didn't say Trezor is the best hardware wallet.
Visit the topic created by dkbit98 and see how the seed extraction vulnerability can cause users to lose their fund.
Trezor hacked (again)

For creating a watch-only wallet in electrum, you must import your address(es) or your master public key. There is no way to import a public key into electrum.
OP must import his/her addresses to create a watch-only wallet.

If you want the fund to be spendable, you can import your private keys instead of your addresses.

You can go for a good hardware wallet like Trezor. That's the best thing you can do. Visit the topic created by dkbit98 to know some other alternatives.
[LIST ] Open Source Hardware Wallets

If you can't afford to buy a hardware wallet or you don't want to use a hardware wallet for any other reason, you can use Unstoppable wallet. Visit the topic created by theymos.
Reminder: do not keep your money in online accounts

Since you referred to App Store, I guess you are looking for IOS version of electrum. If that's the case, note that electrum isn't available for IOS.
You can visit the official website and download electrum for Windows, macOS and Android.

Do not forget to verify your download. Below is the guide provided by DireWolfM14 on how to verify your download.
[GUIDE] How to Safely Download and Verify Electrum [Guide]

Not your keys, not your coins.
With keeping your bitcoin on an exchange, you give full control over your fund to a third party. Even if a centralized service has been around for a very long time, everything is still possible. They may go bankrupt or they may be hacked.


Trust wallet is close source and I would never recommend anyone to use it. We don't know how keys are generated on trustwallet.
There is no guarantee that what happened to Atomic wallet recently won't happen to trustwallet.