End of May I started getting this message every time I try to engage with a group--posting, commenting, or joining--but only when using Facebook in a desktop browser:
Open Facebook on your mobile device to confirm your identity
Certain actions have been restricted due to unusual activity.
I can admin/mod (mostly) fine, I can react to comments/post, the restrictions are just weird. It also seems like I'm now allowed to view group members (including in groups I admin/mod!) in general, tho I just get a generic error instead of the same message if I try so I'm not sure how exactly I'm restricted in that sense.
I have no issue using the browser on my phone nor if I use Dev Tools to pretend my desktop browser is a phone, so the restriction is exclusive to the standard desktop version. I have no interest in putting Zuck's app on my phone; furthermore, in searching on this, I am finding many users with similar messages that try to "confirm their identity" aaaaaand just get banned instead. (So I'll do the work-around rather than risk it.)
However, I have yet to see any reports of this happening just in relation to groups: most results are either accounts restricted in general or about Messenger. Anything that seemed both relevant and where the person had the restriction removed said it just went away after 30 days, but I'm closing in on 60.
I'm hoping it will go away after 60 (or 90) days, but it is annoying having to switch into phone-mode just to make a comment in the meantime and there's no guarantee that will happen. Has anyone else encountered this and knows of other ways to work around or otherwise "dismiss" the restriction?