> newer AVX-512 variants as opposed to older AVX2-only CPUs

This is exactly my issue with targeting AVX-512. It isn't just absent on "older AVX2-only CPUs." It's also absent on many "newer AVX2-only CPUs." For example, the i9-14900K. I don't think any of the other newer Intel CPUs have AVX-512 either. And historically, whether an x86-64 CPU supported AVX-512 at all was hit or miss.

AVX-512 has been around for a very long time now, and it has just never been consistently available.