These days I’m using Ubuntu 18.04 but I had been using VCV Rack on Fedora 23 before moving to Ubuntu. In both cases I’ve used an audio-optimization overlay, i.e. Ubuntu Studio with Ubuntu 18.04 and the Planet CCRMA packages with Fedora.
ubuntu studio 20.04
i also have windows10 on the same machine (laptop, oldish i5 with 8 gb ram) and vcv works far better on linux. i mean i can do more on linux: make a bigger patch, more consuming one, etc.
RHEL 7, on a machine I have no control over choosing distro ;-(
The existing automatic builds only work because they A) use compatible system libraries and B) I wrap Rack in a script that sets LD_LIBRARY_PATH to point to a directory with newer libstdc++ shared libraries.
In short, I’m the worst case for distributing a universal Linux version of Rack, but whatever you’ve set up on your end with the Rack library is working, so I’d be comfortable with you saying you can say Red Hat 7/Centos7 are unsupported.