issues viewing mp4 files on newer gopro

howdy, i only have one computer (work computer, i edit videos off hours because it's my only computer with video software). I have never had issues opening and viewing mp4 files. however, after my friend took some great videos with his newer gopro and we put the files on my machine, it suddenly tells me i need an HEVC codec. These are mp4 files! not HEVC. I cant install a codec on this computer because it's technically work computer and the codec isnt free. Most of the free converters have size limit that's too small. If they clearly had HEVC extensions, i'd understand. but no, they're mp4. I have older mp4's filmed with another gopro that open fine. Has anyone seen this? i cant find anything on google.
Edit, maybe HEVC's ARE a type of mp4, but usually i see it named as such. this looks like a regular mp4 file that i can usually play. i'm a bit of a boomer with this stuff so bear with me.
thanks.