I have a bitcoin core -qt Wallet (on linux). Tell me, can I encrypt it? For example, there is the electrum wallet! It has words for deciphering. For example, i installed the electrum and the phrase was generated. "I'm a fan of the https://bitcoin.stackexchange.com" Knowing this phrase you can install electrum on any computer, and when you enter this phrase you get access to your balance and btc. But what about bitcoin-core-qt? because it is characterized by the fact that the it must download all the transaction history after installing.(~200gb). Is there such a "magic phrase:" for this wallet bitcoin-qt? This is a very useful option if you have lost access to the server or host where you hadthis wallet
You can export private keys from Electrum and BitcoinCore. You can export private keys from Electrum as "words" format (There's a website to convert it to private key(s): https://iancoleman.github.io/bip39/), while Core doesn't have this feature. See the steps in question Using dumpprivkey to make a paper backup to use
dumpprivkey in Core to export the private key.
Bitcoin core does not support seed mnemonics. You must rely on soft copy backups if you want to backup your wallet. The option to backup the wallet file is in the file menu.
If your Bitcoin QT says HD in the bottom right corner then a one time backup is sufficient to get access to your bitcoins at any time in the future. If you care about meta data like address labels you will have to make regular backups.
If it does not say HD then that means you need to make regular backups i.e. at least once every 90 spending transactions.