What is this box that appears in comments? Cleaned cache and cookies, off loaded Facebook. Still there

This is a bug that Meta introduced in one of their many attempts to “make the app better for you”.

It’s for them to fix.

A lot of people have asked about it. You'll have to ask Facebook. They continually release apps with lots of bugs, and this seems to be one. But Apple has nothing to do with Facebook, nor can Apple fix their buggy apps.