Every time I see Ubuntu listed as the "de facto standard" or similar, I realize that I've never seen an Ubuntu server in production.
They're definitely a popular solution, and I'm not sure if I should be surprised I've never seen one, or if maybe it's region / industry specific.
RHEL? Yes. Lots of CentOS, most now looking at Rocky and Alma. A few Gentoo and Arch boxes at smaller businesses. Been logged into the odd BSD, AIX and HP-UX machine before.
Ubuntu? No... Never seem to stumble upon SUSE either, for what it's worth.