I was looking at this issue today (1/06/2025) and out of frustration, I switched the user back to classic Outlook. As it was switching, a survey popped up and asked me why I was switching so I typed in that there are issues with shared contact lists. Once I did that, a help box was displayed stating that new Outlook does not support shared contacts.
Once the switch back to classic Outlook completed, the shared contact list showed up as expected.
WTAF is Microsoft doing with this new Outlook garbage? Crippling the Outlook client and calling it "New" is absolute insanity.
I hope this helps someone