The default ones should be okay. Most of them only are words and numbers together, some of them use _ . I would assume if the devs of the software have used them, that they shouldn't break anything. In addition, most assets I've come across from different authors also used them in their formatting.
So if you want to play it very save you could decide to not use them, but I would say - and _ should be allowed in between normal letters and numbers in most scenarios.
Also, some default files have ! and $ at the beginning. Although it is normally not allowed to use them, RPG Maker in particular uses them to deal with the files in a specific way in the editor. If the platform you want to upload really cares about that is the other thing, but the software has used these two letters since years.
I also have to admit that even though the rules seem to be so strict, it is actually rare that I've heard of people having big problems with their file naming. So I guess not using native special characters of a language and avoiding really bad special characters should normally be enough.