Jeff, thanks for that. Mission accomplished late last night during a scheduled outage.
There's a bit of a 'gotcha' though, when running the 'get-brokercatalog' command to see what it's set to currently, I found that machine catalogs set to '2206 or later' show up the same in Powershell as catalogs set to '2106 or later'. Both are listed as 'L7_25'. I set one of them back to the next lowest level, which is L7_20, and then it showed up in the DaaS console as '1811' for minimum functional level. But, once set to that, I could use the console to choose 2106 which is what I wanted. So, all good in the end. Just a bit confusing when you're looking at the list of MC names and functional levels, and they show up the same despite being different in the console.
Hopefully that tidbit of info might be useful in future, if someone comes looking for the same info!