Apart from the FMP issue, I’d generally recommend against updating to Big Sur (going higher than Catalina), especially on your 6-year-old Mac. First off, for most users (with Intel Macs) BS brings no advantages, but some possible disadvantages: Some apps, not just FMP, may not run as well, or at all, or need upgrading. Bootable clones, IMO still one of the best kinds of backup, are no longer possible. Then there’s the age issue. Even if an older Mac can run BS, it may not be able to cope with it efficiently, resulting in an overall slowdown. Of course, none of this applies to the newer Apple silicone Macs, which need at least BS - and which is a reason for me to not get one of those unless/until I absolutely need to, at least not in the foreseeable future. (That’s probably a moot issue for me, anyway. At my age, given my not-upgradable legacy hardware, I suspect my 2020 Mac will outlast me. ;) )