You can look into fortune 500 report on Server stack, and self published red hat report. Red Hat claims is higher, but I will say, it should be at max 90%, not 95% as Red Hat Claims.
Seems they revise it. hem… the fly-er I got for Red Hat academy promotion written is 95% in 2019… strange…
But anyway, you can see anywhere, on any business medium high, mostly use Linux.
Azure, 100% backed by Red Hat in their Infra, even Microsoft doesn’t deny or agree with it. AWS 100% EL based (old times RHEL, nowdays Fedora), Linode, Scaleway, Contabo, Hetzner, BiznetGio, Aliyun (even their Aliyun/Alibaba Linux is RHEL), OVH, etc. so I will say it’s high enough… that almost entire infrastructure rely on Red Hat Engineering. At least if Red Hat gone, CentOS Stream code still there, Fedora Code still there. The community can continue to develop it.
Ubuntu only popular and first class only on Digital Ocean. No other cloud providers make ubuntu first class other than DO. Sure enough Ubuntu/Debian is there, you can install it, but, it’s not entirely first class as RHEL/Clones
Hate it or love it. Red Hat still the king of mission critical system except in Europe, where SUSE is leading, but SUSE itself is well… have same or near identical to Red Hat… so… welp… kind like in same EL boat.