If it's just Duolingo that's crashing, that's something you should take up with them. They may well need an update to be compatible with the newer Mac hardware and the current version of macOS.
If you're having problems with other apps also crashing and you've worked through the possibilities that Grand provided, then post back with more details and we may be able to advise further.
And if you think that Windows will be more stable, then by all means buy a Windows machine. But I can tell you after having supported both Macs and Windows machines quite possibly for longer than you've been alive that Macs in general are far more stable, and much easier to troubleshoot, than are Windows systems. As with anything, though, there are no universals or guarantees with any human-made thing.
Regards.