You can verify your claimed rewards on the Twitch Drops inventory page.
If the reward has been claimed and your Twitch account is linked, the items should be available in-game.
If the items are not appearing in-game, go to Settings → Debug/Info.
If your Twitch account is already linked, the "Link Twitch Account" button will be replaced with "Check Twitch Drops" — press it to manually sync any newly unlocked drops.
For further details: https://unknownworlds.com/en/news/subnautica-2-twitch-drops-guide