It took me a while to discover this "Easter egg" but my org's logo finally showed up in DEPNotify in Big Sur (even on v1.1.5) after I commented out the command for WindowTitle. It worked in SampleTest.sh and when I compared that with my script, that was it. Somehow the Image command is ignored in Big Sur (both Intel and M1) when WindowTitle is used.
/bin/echo "Command: Image: /private/tmp/ucsf_logo.png" >> /var/tmp/depnotify.log
/bin/echo "Command: WindowTitle: UCSF IT Field Services" >> /var/tmp/depnotify.log
/bin/echo "Command: MainTitle: Hostname: $(/usr/sbin/scutil --get ComputerName)" >> /var/tmp/depnotify.log
/bin/echo "Command: MainText: Please wait while we set up this Mac with standard UCSF software and security configuration. This may take up to 1 hour depending on network speed.
This Mac will automatically reboot afterwards.
Please do not interrupt this process until it's done." >> /var/tmp/depnotify.log