I saw that Colter Bay is still using its existing reservation system and won't be in recreation.gov until next year when they move over.
(googling real quick).... Yea, just looking it up real quick Colter Bay is using gtlc.com (as it has been for reservations) and the other campgrounds that were reservation are still using the same site (gtlc). The sites that were first come first serve are now under recreation.gov. I picked up a spot in Signal Mountain 8:00:00 MST this morning as Colter Bay was already full for the time I wanted.
https://www.gtlc.com/rv/colter-bay-rv-park
"Reservations for the 2021 season at Colter Bay RV Park can be made on gtlc.com, however reservations for these campgrounds will migrate to Recreation.gov for the 2022 season."