I’ve started to use Playnite. It’s nice to have a complete catelog of all my games. Most of my real games are on steam, but I’ve collected a bunch elsewhere like got, epic, humble bundle, and others.

I use it to mark when I completed a game, but I’ve only had it for a couple years, so I generally go by memory or by steam statistics of hours played.

Downside is that it’s Windows only. It’s open source and free, and I still have a windows machine for most of my gpu games, but I mainly game on my steam deck or my Linux laptop these days, so I need to find another option or see if Playnite is wine/Proton compatible.