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.
And using a simple system means that once somebody figures out the system, all your passwords become compromised potentially.
True. But you don’t figure out the system, and if you did, the system could be changed in a matter of minutes. To figure out the system, you would need more than 3 samples of the passwords, at any given moment, and the likelihood of that happening is just about the same as your password manager being hacked, having a vulnerability or you giving people access to it.