Gog Galaxy 2 is the answer. It handles all the libraries apart from Itchio, for Itchio it only handles games installed atm. Xbox game pass is iffy. It worked great and then stopped.
It will launch the installers from Uplay, Steam, GoG, Origin, Epic, Bethesda, Battle.Net to install, for the others you have to fire up their launcher. You can also link the .exe for a game if it doesn’t have a launcher.
It also only shows one entry of a game, and tells you what libraries its in. You can show owned games, installed games and narrow by store too.
This is all all owned games, sorted by release date, there is epic games, steam, itchio, Xbox game pass and twitch all on the one screen. The little screen shows if they are installed, but you can turn that off and the name, or add genre and stuff.
For Age of Wonders, I have it on Steam but also in GoG so it shows 2 up on top and I can choose which one to install.