You will need to install a user script manager extension to install this script.
This script adds on-hover toggle buttons which allow you to grey out (or completely hide) games in the ScummVM and ResidualVM compatibility lists which you already own to get a clean view of what you still have to keep an eye out for.
It stores your data within the userscript's private store via
GM.setValue, so you shouldn't need to worry about your owned/unowned statuses being erased by things like clearing cookies.
It also installs a print stylesheet so printing the collapsed view results in an efficient "thrifting TODO list".
NOTE: On ResidualVM's site, you can't set separate statuses for full-version and demo-version games, since this script uses the short names as identifiers and they share the same short names.