SQL 2022 is only in private preview right now, and testing on a current build of SQL 2022 would really say anything any way, since Microsoft may make decisions between now and the official release.
However, I can still offer an answer from gut feeling and that is that compatibility level 100 will remain supported. With release of SQL 2008, Microsoft established that they would support two compat levels back. That introduced some problems when they released SQL 2012 and they no longer supported compat level 80, and moreover did not support reading backups from SQL 2000.
As a consequence, SQL 2019 can read backups from SQL 2005 and later.
When it comes to the compat level, they stayed with the policy for one more version, and SQL 2014 does not support compat level 100. But starting with the release of SQL 2016, they have not dropped any compat levels at all. My gut feeling is that this will not change.
I'd be curious to know why you are anxious to have compat level 100 around?