I had heard they had rewritten it in go and got a lot more performant, not sure what else they have done. I don’t care much about the politics as long as it’s still open source (is it?).
That said, I’m a happy nextcloud user and I don’t see a reason to switch (after moving both data and db onto SSDs it’s much faster, so maybe php wasn’t the bottleneck).
I guess what they’re saying is, even though it’s “not supported” officially, you can still try and there’s good chances it’ll work anyway. If you need or prefer to stick to a supported configuration, it seems your options are either to switch to podman and figure out nextcloud, or switch away from RHEL.