The screw in fastener tab is broken (pull it out a little more and you’ll see it) else it does not “pop out” like that.
ABS plastic is fantastic for how it works but a challenge to repair. You can google for ABS slur/glue receipt, then cut out/double up another piece of ABS plastic underneath to recreate the mount hole. OR, get a plastic welding kit (hot staples) and weld (staple on) the addition piece. You have extra space underneath so lots of space for margins of error.
FYI, epoxy and many OTC ABS glues don’t bond well but I have not tried everything. It held at first but any bump/stress will easily break the joint.
