What makes cryptocurrencies "quantum safe"?

[Ambatman]

So my questions are:
What makes cryptocurrency quantum safe?
And could Bitcoin be upgraded to be quantum safe?

Nothing. No current technology is safe against a certain level of Quantum computing.
But we ain't there yet. We comparing future with now so a little unfair.

but I'm still wondering what could happen in future and if our BTC funds are at risk.

The world is at risk. Bitcoin isn't a priority. People are just over reacting because of the tag on Bitcoin on it been nigh unhackable.

On the other hand there are some cryptocurrencies that are allegedly "quantum safe".

Bait.

And could Bitcoin be upgraded to be quantum safe?

Yes. Proposals are already on the way though the cost are quite steep.
They are just finding a means with the least cost.

[suzanne5223]

For a few years there are news that quantum computers pose considerable threat to Bitcoin and other cryptocurrencies.

Is either that you don't read the news to understand the content, or it's misinformation news because quantum computers do not pose any threat to Bitcoin; they pose a threat to some BTC wallets due to the wallet entropy.

On the other hand there are some cryptocurrencies that are allegedly "quantum safe".

So, is Bitcoin right from the getgo. Mind you, 99.9% of these cryptocurrencies imitate the BTC concept.

I know there is long way left to for quantum computers to be functional enough to put Bitcoin at risk, but I'm still wondering what could happen in future and if our BTC funds are at risk.

Bitcoin is never at risk, and the only risk is people using a BTC wallet that's not quantum safe. If you use HD wallet now and don't send from the reuse wallet address, you're good. However, you need to avoid other human errors that could expose your BTC to attack.

So my questions are:
What makes cryptocurrency quantum safe?

The cryptography used for the crypro.

And could Bitcoin be upgraded to be quantum safe?

For Bitcoin to upgrade that will be a hard fork.

[Alvin_talk]

Your bitcoin is safe from quantum computers if you do not reuse your bitcoin address, the addresses that will be affected are those that their public keys have been exposed. If you spend from your address, your public key will be exposed, so do not reuse address.

The public key you talking about is the same as wallet address, can't get it.

The truth is many who are new into crypto have this common misconception using wallet address and public key interchangeably whereas as they are not the same thing. To put it in the simplest form, wallet address is derived from the public key apart from script based address which are derived from hashed script.