I can't remember when I upgraded my video card, but I think I was on Monterey, so I don't have a good comparator to BS. But I do think that when I upgraded from Catalina to BS, my Vega 64 took a hit, then when I went from BS to Monterey, it took another hit.
I find that GB is not very reliable as a benchmark program. The variation between scores is very high. I think you need to do multiple tests, in the order of 20-50 repeats to get statistically significant comparisons. I read somewhere that the problem is that GB pauses between tests, so that can affect the scores.
If the scores have gone down in 12.4 vs 12.3.1, I am not sure I've noticed it. I can try running the GB test again when I get a chance. But I didn't measure it in 12.3.1, after they fixed the framebuffer issue, so the only comparison I can make is with 12.3, when we were manually injecting the framebuffers in OC.