Had the same issue. I am happy to mention this in the past tense. After multiple troubleshooting, I got it working.
The problem I had was that the spotlight will not list anything except 'search in web'. The finder items, applications, suggestions, everything was missing. Apart from that Apple Mail was unusable since the Smart folders and search were not working.
I tried, "sudo mdutil -E /" "sudo mdutil -i off " and "sudo mdutil -i on /" and still it was not working.
However, my account that I had this problem was a Mobile Admin account that is bound to my network. I never had this problem in previous upgrades for the whole decade.
Solution that worked for me: Tried the same mdutil commands displayed above, but I did it as another local super user who is also an admin. I'm logged in with the mobile admin account. In the terminal I did "su <<local admin>>". Then tried "sudo mdutil -E /" "sudo mdutil -i off " and "sudo mdutil -i on /"
That's it... after the above commands life was back to normal.
Yeah, same issue. tried re-indexing. still nothing. In fact Does the 'applications' folder in the user profile have anything to with this problem perhaps?
PS, I uninstalled the one drive app today, and spotlight is working 100% again. Uncertain if it is related, but thats the only only change in my software environment.
Since updating to Sonoma, Reminders app search returns null results for items I can see in the list before typing. After reindexing SSD in M1 MBP it can now search up to 1 text character, but very unreliably. As in if I type B .. it will bring up some items. If I add additional characters found in items in the list: null result. Most letters get a null result even if they are the first character of items in the list ... bizarre how broken this is.
Any ideas for a fix other than reindexing HD?