In the days before password managers I created a random password generator CLI program (give it the characters allowed by the website and the length and it generates random passwords). I also had a manually created and edited HTML document where I kept the ID, password, and website link for each account. I stored/saved the HTML file in a password protected ZIP file.
All very laborious and definitely gaps in protection (remnants of the unZIPed version were undoubtedly scattered around my computer’s memory, etc.) Fortunately, this was a couple of decades ago in my pre-smartphone days so synchronizing between devices was not an issue.
I never trusted the “we will save it all in the cloud for you” paid password managers but when I became aware of KeePass I jumped on it. I have gone through various KeePass app/programs on several platforms seamlessly. I synchronize it between devices via my NextCloud server.