In Steam, go to Properties > Local Files > Verify integrity of game files .
If you’ve tried the above and the DLC still won't "work," your save files or game metadata might be corrupted. oxygen not included dlc unlocker work
If you are in "Base Game" mode, you won't see any DLC features like rocketry or radioactive biomes, even if you own it. 4. Resolving Mod Conflicts In Steam, go to Properties > Local Files