Windows 11 Pro 24H2 OS Build 26100.2605 PC will not in sleep or hibernate

I titled this under W11 update since it's only been happening since I got the above stable.
Having got rid of an unstable W11 "insider" version and the update to my BIOS for the Intel Core Ultra 7 -265K CPU (I only game occasionally) I finally have a stable system. Unfortunately, although my PC appears to sleep and hibernate without issue, it wakes up during the night and lets me know its done so.

I have unchecked Wake on Lan in case my server (same OS) is causing it, but it still happens after about 3-4 hours of no use.
Screen time out is set at 15Mins.
Sleep at 1hour and hibernate at 2 hrs.

It no biggy to shut it down at night, but why won't it remain in sleep / hibernate?
Server is in the basement; I'll check if that ever goes to sleep....