Quantum Computer can't stop the high security of Bitcoin. There will be no additional security on Bitcoin than the highly recommend securities of Bitcoin. You can secure it offline and online with non custodial wallets. And don't keep your long term investment Bitcoins in exchange or custodial wallets.
No. You are wrong. The threat of quantum computers is real and just so you know, it doesn't only pose a risk to BTC, but any cryptographic system; the good part is we are at least 20 years behind the reality of this threat. Securing your coins offline or in self custodial wallets does not protect you from the threat of quantum computers, except if you have not
spendspent from the address that holds your funds, meaning the public key is unknown, so QC cannot derive the private key from the public key.
Quantum resistant algorithms are going to be tested and implemented as we progress
and. And before this threat becomes real, we should have migrated over to those algorithms.