Users needed to test Wi-Fi stability on Linksys WRT3200ACM & WRT32X on OpenWrt 21.02

That should be relatively easy, but it won't buy you much - v5.7.x was not an LTS kernel, its maintenance stopped in late August 2020 - no bugs (security or otherwise) have been fixed or even tracked beyond that. As maintenance of stable (or LTS) kernel isn't quite linear, after all development happens in linus/ master and is only backported later, it's not very likely that going from 5.7-rc1 to 5.7.19 would gain you more insight (especially with the short attention span it has gotten).

The elephant in the room remains that v5.7 is functionally speaking a dead-end, downgrading the wireless subsystem to that state will only work for kernel v5.4 - with master already being on v5.10, it really should only be used for debugging (and maybe as a temporary band aid on the road towards a proper solution), but it's not (and can't be) a long(er) term fix.