it's already been tested by another staff member so unless it needed re testing, i can't see it being added again to my list.
not fully sure 100% of all the questions, but my take on it would be,
What does "stretched full screen" mean?
Does it keep the same aspect ratio but everything appears bigger?
Or will it stretch and distort the image a bit?
Any performance / Alt + Tab issues?
What does "stretched full screen" mean i'd say it works in a windowed mode that can be altered or made to go full screen as it may not fully support all native windows 10 screen resolutions etc, running them in windowed mode them pressing the minimize / maximize button in this mode sometimes stretches the window to a larger than standard size so makes it look like a full screen instead of a windowed box eg smaller screen, but maybe wrong.
Does it keep the same aspect ratio but everything appears bigger? this is more guess work, but normally if you run in a stretched window box, then some things can look bigger on a smaller size box, but once stretched to almost full screen, can make them also sometimes blur, but not always, text can alter more than icons etc, but same is true if you alter DPI, as the larger or more dots per square inch, on a none supported hardware picture can make it looks blockier on some none native resolutions, but not all, so you may have to play with a few settings to look better, as some will be worse.
Or will it stretch and distort the image a bit? covered some of this in both above comments, and depends on default users resolutions tbh, so no real correct or incorrect answer on this one i'm again sorry to say, but of hit and miss and user time needed to get right, doesn't suit or work in all sizes.
Any performance / Alt + Tab issues? normally box user or windowed mode is quicker by a long way, and as these are older games anyway, sometimes it can be too quick, but again that depends on hardware and game in question, alt tab shouldn't be an issue as that's normally the first thing in game that gets tested, run as admin, with the min of apps running, plus add game exe to firewall and AV program so it runs in it's own space etc, with full permissions and alt tab only ever affects an odd game or program, then running in a native mode or one of the compatibility mode settings normally corrects this anyway, but not fully known on this one, can't ask either as i don't know who tested it either or i would