Use an out of band password manager, whose key is never transmitted over a network. Or a notebook that is physically secured. There are a number of solutions for password vaults, and you can use a variety of means to synchronize them if needed.
The notion that it's a good idea to trust a browser extension for secrets management is pretty bizarre to me if you're protecting high value assets.
As always, it depends on your threat assessment and what is practically possible. For the vast majority of users, using a password manager browser extension [1] is a large improvement over password re-use over dozens of sites. Most folks will also not want to put in the effort to use an out-of-band password manager.
(Not directed at you personally, but I often hear such comments from people who are then perfectly fine to use a password manager in X11, where in a the default configuration every application can read your keystrokes, screen grabs, clipboard, etc.)
[1] Preferably one that communicates with an out-of-process password manager over an authenticated channel like 1Password.
I love passphrases and mnemonics. There are passwords that I retired out of anywhere they existed several years ago that I will probably never forget as long as I live. And not only is it easy to create memorable passphrases, and they're fairly long, you can then combine your passphrases in interesting combinations to get even more passwords that you probably will never forget.
Beyond that, the "never reuse passwords" adage is horribly oversold. If it handles my money, my email, or my web hosting, it needs to be unique. Passwords for places I comment are commonly reused and not as sophisticated because it is not seriously impactful to me if someone gets a hold of them.
Reuse passwords for sites that can't meaningfully harm you if they get compromised. Minimize how many accounts can harm you by not saving your credit card info in most of them, uncheck that box when you pay for stuff.
I'm also insanely liberal about deploying 2FA. I have it everywhere it's available, even sites with common/stupid passwords. So a lot of sites I don't bother with unique passwords will still be somewhat protected if my password is compromised. I'm also subscribed to haveibeenpwned with every email address I've ever used for anything.
The notion that it's a good idea to trust a browser extension for secrets management is pretty bizarre to me if you're protecting high value assets.