Synced Lists

https://www.steamgifts.com/account/settings/giveaways

Setting #2:
Hide games you already own?
[✅] Yes
[ ] No

-> Save Changes

Profile features limited are new games from smaller studios before they reach some threshold of sales. You'll see such label on steam together with other features like cards, achievements, etc (They used to be tagged "Steam is learning about this game")

As for the settings, unless something changed I'm quite sure that hiding owned games is the default. Just in case you may verify your selection in settings: https://www.steamgifts.com/account/settings/giveaways

Another reason why a game might not be hidden is because you hadn't synchronized your library yet. If I'm not mistaken sync happens automatically only once a week, but you can trigger it manually from your profile page as well: https://www.steamgifts.com/account/settings/profile
This may lead to games you recently acquired showing up in the GA list just because the site doesn't know yet that you own them. But same would occur for newly wishlisted titles. Before you sync they won't be visible in the wishlisted filter