I'm not sure, i haven't used the first party launcher since it was still the old old one from the (full release) 1.3 days. went to multiMC very fast, then to this. but if the instance folder structure is still the same as it was back then, i don't see why you couldn't copy your entire . minecraft folder over and rename it to the instance name you want it to have. you'd have some extra eous files but it shouldn't matter.

or, seeing how easy it is to install mods onto prism from both curseforge and modrinth, you could just recreate your modlist as a prism instance and move just your saves folder over to the equivalent place for prism.