I have never used a PW manager. Never have, Never will. I have my own code system learned back in the 1960’s. I would tell details, but then I would have to kill you.
So long as your passwords are at least 12 and preferably at least 15 characters long, have a mix of alphanumeric and punctuation, are all different from each other, and written down somewhere/someway so that when you pass on someone can get access as needed, then I guess you’re good to go. I have too many passwords to memorize them all, so I use a password manager to manage the above conditions and I just remember the password for it.
My system has all of that, and more!