A single client to run games from different clients [closed]

Solution 1:

There are some custom clients that try to solve this problem, for example this one:

https://www.steamgriddb.com/manager (I'm not affiliated with it and not using it):

Currently Supported Launchers:

Origin
Uplay
Epic Games Launcher
Blizzard Battle.net
GOG.com

It doesn't allow you to actually buy games, but you can browse and launch them from single place.

Disclaimer: it's up to you to decide if you trust such services enough to install them / provide your credentials / grant file system permissions, see Malware.