Please differentiate between two things:
- does your R7800 boot-loop with the default settings?
- or does it boot-loop with your personal confoig, with added VLAN settings?
Serial access would be crucial, as otherwise you do not see the kernel log at the crash time, so it is pure guessing what causes it. It is pretty easy to enable in R7800. See Netgear R7800 exploration (IPQ8065, QCA9984) - #2 by hnyman
And @Ansuel is actually the person doing the hard work here with kernel 5.10.
Personally I do not use VLANs, so no comments regarding that part. The build has worked for me.