I would say boot from the Rocky 9 DVD or minimal ISO image, you have options there I’m sure for booting rescue mode. Not sure why that’s not working, as that was always the way to do it with EL7/EL8 versions.
EDIT:
Yep, is a bug:2057365 – Unable to reset root password using rd.break there are some alternative methods suggested there. One of which suggested, instead of selecting the normal kernel to boot with, from grub there is the rescue kernel, select this, then edit this and add rd.break and boot. That apparently should work (reddit post also hints at this). Other suggestions involve adding init=/bin/bash but never used it personally.
EDIT2:
I remembered posting an alternative using systemd.unit=rescue.target when editing the grub entry temporarily like you do with rd.break. so another way around it: Autorelabel and SELinux Question - #5 by iwalker