Blizzard has announced that today's 9.2 PTR update is the final full build of 2021. There may be some hotfixes coming to the PTR before the end of 2021, but the next large build will be scheduled for January 2022.
Blizzard While we don’t typically publish a full testing calendar as we proceed through each PTR, we want testers to know that today’s PTR update will be our last full build update for the month of December. Read more on wowhead.com