what role do unofficial ports have on the official app loader?

Hi - I have zero problem with those other apps being used on different devices, as long as the method of doing that doesn't make life more difficult for Bangle.js users.

So, is it true that this file is the hurdle to allow unofficial ports to use the 380 apps?

More or less - many apps have hard-coded screen sizes and stuff like that which could make it more difficult, but quite a few should work fine.

Getting jswrap_bangle.c built in would definitely be the best option (it already supports at least 4 different watches, so adding more shouldn't be that bad), but if for some reason it was hard I guess you could fake most of the functionality (slowly) in JS.

for those 380 apps, is it the same? with reasonable porting(exclude those that need the above file), i could run them on unofficial ports?

Yes - although obviously maintaining a port of 380 apps is unlikely to be feasible.