If you could download an already synchronized state, you shouldn’t do that. The purpose of synchronization is to produce a valid database containing the state of the network, downloading somebody else’s can have false entries and your node would not know that it is invalid. Increasing the dbcache can improve performance but you don’t have much additional ...
There’s simply no support for using the Bitcoin-QT application as a RPC client, it needs far more access to state than is provided by that interface to operate.
There’s no real reason to try to separate users like that either way, if the desktop user has access to RPC, what is the difference to it just running the daemon itself? Assuming that loss of the ...
This is a BIP173 native segwit address.
If you unselect the "Generate native segwit (Bech32) address" checkbox in bitcoin-qt, you'll get a P2SH 3xxx address instead. Most senders these days support sending the BIP173 addresses though, which are cheaper for you to use.
The GUI no longer supports creation of legacy 1xxx addresses by default. You can ...
Yes, after you've checked if bitcoin is properly "installed" by checking its version you can remove the ~/Downloads/bitcoin-0.20.1. Be sure to double-check the processes and be careful before putting funds in without backup.
From what file does bitcoin-qt get the information about the old wallets? How can I stop this behaviour?
Open settings file and remove wallet name mentioned in error.
There's no particular issues with running both the daemon and the QT using the same data directory, you're also protected against running them both at once due to locking. Most versions, especially within a single major release, are compatible so there's no burning concern about keeping them exactly in sync with one another.