Update 5/24/2022: We have now enabled all of the cmdlets to be REST-backed if you are using the 2.0.6-Preview6 module.
We’re excited to let you know that we are working on a new version of the Exch...
Updated May 24, 2022
Version 12.0
Blog Post
MrPink99 the PowerShell warning stream is what it is, and shouldn't be allowed to cause your program or script problems. That's not playing by the rules.
While I do agree the warning is pre-mature because the preview version is all that there is currently, vs a GA version of what is being advertised, I don't think anyone writing PowerShell can be held accountable for their warnings done the proper way causing this kind of issue. The issue is that you're doing screen scraping and if that can't handle PowerShell warnings then your solution is the one that is flawed. It's not the Exchange Team's fault, as unfortunate (and unnecessary) as it is.
As far as I can tell the warning happens only once per session (per Connect-ExchangeOnline). Maybe you can use that behavior to your advantage and put in a dudd command to force the warning to come and go, then get back to the task at hand in the script/app?