That message in the Welcome Screen is always there whether you have a backup or not.

The question is, are the contents of mnt/61CCC2CO311E1DCA/Bitcoin the data directory or just the Bitcoin Core binary?
Because usually, the datadir starts with a lowercase "b" instead of uppercase "B".
Also, if your old setup is "pruned", you'll have to set the new setup to prune with the correct size.

To be sure check if it contains a "blocks" folder, if it's there, check the contents if it reaches 500GB+ of data.
Also check if there's a "bin" folder inside it.

You need to keep the exact data directory so that Bitcoin Core can "see" that there's nothing changed.
"Exact" as in including the wallet.dat files and other files in it, not just the blockchain or Bitcoin Core.

For example: if you're using the default data directory, paste the old "bitcoin" folder into the same directory and Bitcoin should just continue to reach the tip without a reindex.
If you've set a custom datadir in the GUI before: in the "Welcome Screen", point to the directory where the "bitcoin" folder is pasted.

Freeze is the only way to accomplish that unfortunately.

You can utilize rebalance to reduce a channel's inbound capacity by sending your other channel's amount to it so that it can't be used to receive until it gains inbound capacity again.
Selecting two channels using CTRL-click will enable the grayed-out "Rebalance" button.
You can also setup channels to Electrum's trampoline nodes and others with normal nodes so whenever you disable "Use trampoline routing", your channels with trampoline nodes will have their send capacity frozen.
But those are more inconvenient than just freezing the channel's inbound/outbound capacity.

AES with your master public key's various hashes: github.com/spesmilo/electrum...plugins/labels/labels.py#L32-L48 & /labels.py#L188-L192
The "data" by the way is just your labels, not a security issue but privacy rather.

Quantum... Aren't those just supercomputers emulating quantum computing?
(I don't know much about those, don't answer, it's off-topic)

Additionally, with trampoline nodes enabled, you're limited to the hard-coded trampoline nodes so by opening a channel with them, it's already a given that you're using Electrum.

For recoverable channels, you're also correct.
There's an additional data in the form of OP_RETURN which usual open channel transactions doesn't have.

If you decided to follow the "restore seed phrase" route to circumvent that limitation,
you can enable "Label Sync" plugin in the settings so that when you restore the wallet from seed, it'll restore the labels as well.
The downside is your data will be stored (encrypted) to a central server.

Was the issue the button being grayed-out or it returned with similar "no UTXOs" message as Green?

If the former, the recipient address/wallet below may not be auto-filled, selecting an active wallet should do the trick.
If the latter, there's only one reason that it didn't found any UTXO: the server that you're connected to may be missing those UTXO.
Additionally, you can't be offline at that time because otherwise, "Sweep Private Key" wont be clickable to access that window.

In Sparrow, was "Create Transaction" unclickable?
Because it wont be if there's no loaded wallet or address in "Sweep to:" where the bitcoins will be swept.
Or was it in the next steps?

In Blockstream Green, 'sweep' isn't available.
Sweep in Blockstream Green for Android seems to be non functional since I'm getting the same "No UTXOs found" message. (may be a bug)

For testing, you can use "Regtest" which can be set-up in minutes and mine blocks in seconds.
You can read more about it in the developer reference's "Testing Application" page: developer.bitcoin.org/examples/testing.html

You're correct that it's not part of Electrum but my best bet is it's the sound that I've mentioned above.
It's part of Window's alert when the user is clicking outside of the active window which wont be disabled by muting Electrum's sound in Volume Mixer.
I'm guessing that his bot is double-clicking or mis-clicking somehow.

As an addition to my post, it can be muted by setting the "Default Beep" sound to "none" in System Sounds.
Shortcut is in "Search->type and click: change system sounds->Scroll-down and click: Default Beep"; below, replace the default "Windows Background.wav" into "none".

The balance should be displayed at the lower-left without needing to click the "green circle" (when all on-chain confirmed) balance distribution icon.
Also, there shouldn't be any sound associated when closing that window.

Does the sound similar to Window's "Asterisk" sound file? (Google for reference)
Because if so, that'll play in Electrum if you mis-clicked anywhere in Electrum window but outside of that balance window instead of the 'x' icon or 'Close' button.
(try to reproduce it manually)

For SHA256, try any input in this website and judge if the steps are possible to reproduce by hand:
Link: https://sha256algorithm.com/
The buttons at the right-hand side of the input control the steps.

If Air-Gap cold-storage setup isn't an option, you can consider 2FA Electrum which is categorically safe.
It requires a 2FA device which should be your phone with Authenticator app and (third-party) additional service fee for the 2FA service.
As long as you keep your seed phrase safe and generated it offline, your wallet will be safe even if the computer/wallet gets hacked.

For information and security reasons, you must read and follow the suggestion in Electrum's 2FA wallet setup wizard:

Image from: electrum.readthedocs.io/en/latest/2fa.html

It's possible if you can mimic Electrum's connection with the servers (it's open-source): github.com/spesmilo/electrum/blob/master/electrum/network.py
For example, there are other clients/wallets that can use Electrum's server like "Blue" and "Sparrow" to mention a few.

But as mentioned above, most Electrum server implementations have even smaller limits than blockexplorer APIs, which is set by default.

I second that Windows Defender may be removing the file as hashtopolis client downloads it.

I'd suggest you to add an exception to the whole working folder "C:\Users\Studio\Desktop\New folder",
by following these steps: support.microsoft.com/en-us/windows/add-an-exclusion-to-windows-security

There are "external signers" to be able to use Bitcoin Core with your hardware wallets but it's tagged as "experimental".
If you want to know more, read the documentary about it in Bitcoin's GitHub repository: github.com/bitcoin/bitcoin/blob/master/doc/external-signer.md

...As you can see, it's not end-user-friendly.

Are you running your own server?
e.g.: "Electrum Personal Server", "Electrs", "ElectrumX", etc.

For the setup, follow this tutorial from Electrum's official documentation: https://electrum.readthedocs.io/en/latest/tor.html

The wallet file and electrum data directory which will be stored in the persistent drive will not contain any data that'll compromise your Trezor.
In worst case scenario, an attacker can only get access to your transaction history.

Was v4.0.9 had the same error? Because I might have misunderstood that part in the OP.
If so, the commit that I linked might not be the cause of issue.

Is it SegWit? Try to use Electrum v4.3.2 if the issue will persist.

If not, it may have something to do with this Commit: https://github.com/spesmilo/electrum/commit/d3227d7489fe327bd40e891a517c86bd207227ec (in v4.3.3)

If still there, enable logging and check if it has something that's related to the error.
You can enable logging in "Tools->Preferences->Misc->Write logs to file" (restart Electrum), reproduce the error and then disable logging.
Log is in "logs" folder inside Electrum's datadir (location).

That'll be a long shot, he needs more than his node's IP and port in order for you to connect to his node.

For the server, it's the latter "electrs": https://github.com/romanz/electrs (but there are other options)
There aren't any available binaries so he'll have to compile it himself, go to "doc" for the instructions.