Just to make sure, the game is still not downloadable, right? Key redeeming seems to have worked fine, I just have to wait until January 12 for the game to be available on Steam?
You get a Steam key! You get a Steam key! YOU get a Steam key!
Want a "Buck Up And Drive!" Steam key to go with your Itch purchase? Of course you do, don't lie to me! Here are some simple instructions on how to get it, depending on your situation with Itch:
Have an account on Itch? Check your purchase history, you should see a button to redeem your key on the game's download page!
Don't have an account? Now there are two possibilities.
If you still have the email that got sent from Itch, use that to access the download page as you did before. You should see a button to redeem your Steam key! Don't have that email anymore? Itch Support Page to the rescue! See the "Recover purchases" option? Slap your email address on that, it should get you sorted.
What's that? Redeem button ain't working? Probably ran out of keys, those are added to Itch in finite batches. Just let me know and I'll look into it!