I can't seem to find an achievement list for any games that have them. I found some that show "popular achievements" but no full lists for those games.

Also have a ton of games in my collection, but most are without achievements. Would there be a way to see just which games I own that have achievements?

In Galaxy, click on the game, [My Progress] tab at the top, and that's where you can find all your achievements.

You can usually tell if a game has achievements under [Game features] of the store page. For your library, you can tell if a game has achievements if it has a #% in Galaxy with the trophy column. Blank values = no achievements.

Screenshots here: https://imgur.com/a/lKZWIsI

Two ways to go about it outside of GOG Galaxy:

1. Hover over your name in the menu at the top of this page, then click on Your profile.
2. On that page, click Games, in between Profile and Friends.
3. On the last page, games that have achievements are marked with a trophy icon followed by completion percentage. Games with no trophy icon don't have achievements.

1. Hover over your name in the menu at the top of this page, then click on Games.
2. On that page, click Features, in between Language and Tags. In that menu, check Achievements.

For games that you don't own, I'm not aware of any method besides a third-party site like ExoPhase.

Thanks to both of you!

Exactly what I was looking for.

Wonder though why the features filter is not in the Galaxy client.

edit: Odd. When I click on the achievements filter, it does not list all of the games. Such as Deus Ex I noticed does have achievements based on my activity feed, and seeing it unser the my progress showing the achievement list. However it does not appear on the achievement filter. Oversight from GOG I guess.

Looks like I might have to do this the hard way. Go through 700+ games on by one to see make a list.

edit #2: So looks like I might have a solution to the galaxy end. So Galaxy does let you sort by achievement percentage. I was a bit wary of this when I first tried it since it listed every game I own. this includes those without achievements. Of course putting higher earned achievement games up top. I noticed though for games not with earned achievements but that did have them were also up top, and games without achievements toward the bottom. I found the cutoff since it appeared the games are alphabetical also. Meaning, through this list it descends like this:

1. Games with achievements earned 1st ordered by percentage of completion
2. Games with achievements that have not been earned ordered alphabetically
3. Games without achievements at all ordered alphabetically

So this helps I guess determine and allow me to make a list easier in Galaxy with tags.

If using the site, you'll probably want to stick to the first method I described. I encountered numerous filter problems like the one you mention with the wishlist, so I wouldn't be surprised if it also applies to the library page (I don't use it enough to notice). The response from support has been to either act like the bug isn't an issue at all, to apologize for the inconvenience, or to pass the report to the relevant team. In all cases, the end result is that the problem is never fixed. To expound a bit more on what MeowCanuck said above, step-by-step directions are basically this:
1. Click Owned games on the left sidebar.
2. On the right, click the View icon that looks like two sliders, the one in between the Search button and the Minimize icon. From there, select List view. In the Customize list view submenu, make sure Achievements % is checked, then choose Sort by: Achievements % and Group by: Don't group.
3. The trophy icon column is Achievements %. A blank row means the game doesn't have achievements.

Deus Ex may be a weird case because its achievement list belongs to an official mod.

https://www.gog.com/game/deus_ex has never had achievements.

https://www.gog.com/game/deus_ex_revision does have achievements.