most of my games are through steam, and there's some overlap due to some games i bought on steam requiring uplay and also gog connect bringing steam games into gog. i’m probably not the only one, so what is everyone else doing with duplicate games? is there a way to combine them? do you hide all but your favorite platform? something else?

I hide the duplicates.
As to which one I hide depends on the platform it uses. For example, if I bought a Ubisoft game on Steam, I hide the Steam entry, so when I launch it Galaxy does not have to start Steam AND THEN Uplay on top of that.

Also, I noticed that some Steam-GOG duplicates make Galaxy think that those GOG versions have achievements even though they don't. Saints Row: The Third as an example. The GOG version does not support achievements according to its store page.

whoa there's a source column! i made my window as narrow as it would go and that column had disappeared. i might leave the duplicates for now since i typically just look at my installed games anyway unless i’m looking to install something.

I'm just leaving the duplicates where they are for now. The new way it handles dupes (it shows the associated client on mouse over) is okish. I would rather every game tile had a client icon in the top corner. It would be so much easier.