I rechecked my links and found this: https://github.com/Atmosphere-NX/Atmosphere/issues/813#issuecomment-696592650Thanks!
This guy is having the exact same problem, just on a lower CFW version and firmware. Are you using MacOS to setup your SD perhaps?
In any case, boot hekate before Atmosphere and run the archive bit fixer from its tools. If you need a guide how to setup with chainloading fusee through hekate, refer to an applicable guide from here (have to know your Switch model): https://rentry.org/CFWGuides