i would love epic launcher games library check

I'm not aware of Epic providing API that could be used for manual check. They even have really bare bone profiles and it's not possible to check things like game achievements without opening the game and going into overlay...

You can always compare what you own on Epic and then click on eye icon next to the game name to hide it. Same for other platforms where you may own games
https://www.steamgifts.com/giveaway/MqQQy/company-of-crime

First of all you need to ask Tim Sweeney to provide needed api on Epic Store. Considering how much it took them to add shopping cart - I think it will require at least 10+ years. When this requirement is fulfilled we can return to this discussion.

gg.deals can generate a list provided you added your claimed games manually to your collection. As MSKOTOR wrote you'll have to hide specific giveaways manually on SG.
-link removed-

At this point can't you just use GOGGalaxy and check all the plugged launchers at once?

You can use ESGST to hide anything you want. Though it's not automatic.

I use Playnite and have a little script that can write the steam urls of all the selected games to a text file. I then dump the links into ESGST's Hidden Games Manager to hide all the games with a single click.