Yes, you can "upgrade" from Mojave to Big Sur. But three things to consider:
1. You need to make sure that all your third party software is compatible with Big Sur. This site can help you with that:
Crowd-sourced application compatibility for macOS, iOS and Windows.
roaringapps.com
2. It might be better to do a clean, fresh installation of Big Sur, instead of just upgrading "in place". That's because you are skipping an intermediate OS, Catalina. I've read both positive and negative stories about skipping one (or more) mac OS with an upgrade. Myself, I always top a clean, fresh installation of each new mac OS. Helps me avoid any issues.
3. It's best to wait until at least the .1 version of the new OS comes out before upgrading. That's because the initial version typically contains a number of bugs. Again, though, the version you upgrade to will depend on #1 above.
Of course, it goes without saying that you need to making backups frequently to an external device. You are doing that, correct?