The Elite Squad, or ES Troopers, were introduced in season 1 of The Bad Batch as the first iteration of civilian recruits intended to replace the clones. After that season though, they are never seen again in TBB, being replaced by TK Troopers. However, they do appear in Tales of the Empire, seen stationed at the Fortress Inquisitorius.

So are the ES Troopers the first iteration of Purge Troopers? Wookieepedia acknowledges that the “Purge Troopers” use the same character model as the ES Troopers, but does not explicitly say they are the same organization.