You may want to make sure with your dealer what they can get you. I had to have them confirm for me before making a decision to go in a different direction.
I was in a similar situation. Local dealer first said they could order it, then they could find it. Bottom line was that they could not get the truck we wanted, said they could work out a trade, I kept finding trucks on the chevy locator only for the dealer to tell me they could not work it out. Got frustrated with the dealer. Evidently these trucks and the backup for lost production from shutdowns has the 2020's in short supply, and so dealers are not trading them to other dealers. I actually had a better equipped truck than the one I bought found exactly how we wanted it just 2 hours away from home and the dealer I was trying to work with cost me on that one by not being straight with me. We ended up going to Ohio almost 8 hours away to get our 2020. I located the truck the day it showed up in transit and worked out a deal and put a down payment on it over the phone a day or two later. The closer truck had a couple options I wish I had in our truck.
I asked a different local dealer about ordering us a truck and they told me orders would be for 2021's at this point and would be 6-8 weeks out. Also said that pricing and rebates would be with what was at that current time when the truck arrived. That was about 3 weeks ago, so I am guessing unless something has happened to dramatically change availability of 20's, that you would be buying a 21. She also told me that the current promotions are likely to be much better price points than when the 21's start to hit, which I already knew.