Hi - yes this index issue is a right pain!
There are two sets of indexes that are reported - one from WIN11 which indexes all your files, documents etc and you can see this in Settings/Privacy & Security/Search Permissions/Searching Windows
The other one is the Outlook Index which you get in Outlook /Search/Search Tools/Indexing Status
I have found that I have to leave my PC running for at least 5 hours before it goes to sleep, I send the screen to sleep after a few minutes. It seems that the indexing does eventually work but it is quite slow and never is able to cope if your machine goes to sleep soon after you finish using it. I initially left mine running permanently for a couple of days before the items remaining to be indexed dropped to 0. By trial and error I found that leaving the power sleep mode to 5 hours meant that I am usually fully indexed most of the time.
Jo