The password managers are: KeepassDX (Far Left), KeepassXC (PC version of local), Proton Pass (Better privacy) and Bitwarden (Far Right). Please note that bitwarden does some data collection. See their privacy policy here and their privacy spy rating here.
There’s a principle in security, https://en.wikipedia.org/wiki/Kerckhoffs’s_principle, roughly summarized as “the enemy knows the system”. It’s the notion that you should be able to fully describe everything about your system except the secret key and still be secure.
That’s always a concerning thing to encounter at the beginning of a description. That implies that there’s an awareness that if you knew how the system worked it would be weaker, which in a security setting is considered a very notable defect.
If we’re looking at the actual security of the system you describe through that lens, the name of the company doesn’t add to your security. Neither does your word substitution rules. The secret in your system is the passphrase and the number you’re using to modify the letters from the company name.
Now, using a passphrase is good, but it kinda felt like you were implying that you use the same passphrase for all services and then modify it. That’s not a good idea, since it reduces your effective security to a single number.
Additionally, a passphrase should be random words, not a known phrase. If the phrase is grammatical it reduces the security pretty fast since it’s weirdly easy to guess word sequences.
Adding a character to the end of a password during rotation is also a bad idea. Anyone breaking a password database will automatically try with a series of characters tacked onto the end specifically to catch that, so a password of yours that got leaked years ago can be used to figure out your current password just by checking it with different endings.
A better system would be to write a truly random password down on a sheet of paper along with 31 others. Now fold up the piece of paper and put it in your wallet.
You are already adept at keeping paper in your wallet secure, and anyone not in physical proximity to you has to fall back to the usual tricks to get at your stuff.
Better yet would be to use a password manager, ideally one you can export to something you carey, encrypted, with you while you go.