What does that even mean? I doubt you can forbid the usage of personal messaging apps except in very exceptional cases (like a court room).
On the other hand: Using personal messaging apps for work related information is a no-go anyway because of confidentiality agreements basically everyone signs.
- Ban ANY use of your personal chats / device at work (eg. your wife texts you to bring milk on the way home)
- Ban WORK communication (eg. My colleague don't understand recent commit I've made)
So the web really isn't explaining how things enforced or what is being done. I do know of some industries where you put your personal phone when entering specific locations or having stickers on cameras) but here I didn't fully understood the scope.
Now the idea is all banking related stuff is done on approved devices and clients so you can deal with retention(more like deletion) and loss.
And no personal chat clients too. If you're low enough on the pole, you don't even get to keep your personal devices with you.
You can forbid your employees to use non official apps to send work related messages for privacy, compliance, security and other reasons.
I don't think this is legal in EU but for that kind of low-level work they tend to get away with that.
I see no EU regulation that would give employees a right to play with their phone on the job.
However this company was super abusive anyway. Putting pressure on people to work nights and weekends etc. It was a subcontractor.
In the end meta replaced them all by AI moderation and fired thousands of people in one go.