Additional chat-related features and issues within Microsoft Teams for business
Some additional info for people who've been replying to this thread.
The issue isn't so much to do with Teams as it is the Windows 11 operating system. I've confirmed this by testing on Windows 10 & 11 and with the new & old Teams clients. I've also confirmed this by encountering the same poor spelling suggestions when filling out forms in the Edge browser on Windows 11.
It just happens that Teams uses the OS's spellcheck and not a dedicated spellcheck mechanism like desktop versions of Office products do.
Now, you can go into Edge settings, and change the "Enable grammar and spellcheck assistance" from "Basic" to "Microsoft Editor" - for improved spellchecking in Edge - but, that doesn't carry over to Teams unfortunately.
Also, I received an update for the case I have open with Microsoft support: "...the latest the fix can come is late February or early March..." and "The fix could come sooner"
So, yeah - pretty vague still. But its in the pipeline and should be coming out the first quarter hopefully.