Use the "passwords" feature to check if one of yours is compromised. If it shows up, never ever reuse those credentials. They'll be baked into thousands of botnets etc. and be forevermore part of automated break-in attempts until one randomly succeeds.
That is assuming that someone will sit there and try to decrypt password rules for that specific person. Chances of that happening are basically 0, unless they are some sort of a high interest person.
If there's a leak with multiple services, it's possible some script kiddie will flag it as having a pattern. I'm guessing the rule is simple enough that an unsophisticated attacker could figure it out with several examples.
It's way better than reusing passwords, but I don't think it's better than a password manager, and it takes way more effort esp given all the various password rules companies have (no special characters, must have special character, special character must be one of...). If you're paranoid, use something like keypassxc that's just a file.