The problem is how many random characters can you remember in your head?
A good encryption key would be around 32 characters to form a 256 bit encryption key.
You can do a fun game of encrypt the encryption key with a password but that's just another vulnerability in the chain.
I recommend getting a PGP key stored on a yubikey and then encrypt all your notes with it since it's all in markdown, I store my notes on Google drive and keep them decrypted in memory so that I can still use Obsidian.
As long as you protect that password store with a sufficiently strong password that you store in a password manager that has a sufficiently strong password :P
I joke but yes some sort of password store is what you would use but make sure that password store needs something like a yubikey with a strong private key on it ^_^