I’ve heard reports of the screw backing out on these motors. Has anyone had the screw from where it’s missing in the picture back out. If so, what’s the solution to keep it from happening?

Yes, it is a known problem with some (depends on SN) 2021 engines. Mine backed out as well as at least 5 others that I know of on the NPFL tournament trail.
Check it regularly and you can remove and add lock tite. Be sure to not rotate the pin as it is slotted where the bolt goes and it affects the trim sensor.

Vibra-TITE VC-3. You can thank me later.

Been there done that. Get you a stainless steel bolt with a locking nut and not worry about it no more

Yepp, happened to me.

Mercury has an updated part number that will hopefully fix the problem with plenty of loc-tite.
They were back ordered but saw where European marine got some in.