Comment 1 for bug 1976249

Thank you for your bug report. The script isn't part of upstream xorg-server, where did you see that --auto-servernum has been deprecated?

The script for Debian (and such Ubuntu) is on
https://salsa.debian.org/xorg-team/xserver/xorg-server/-/blob/debian-unstable/debian/local/xvfb-run

it seems fedora also has a copy which they patched some years ago to mark that option as deprecated and add auto-display instead, unsure what was the motivation behind the change though
https://src.fedoraproject.org/rpms/xorg-x11-server/c/9e2c5679