I have the same problem. This appears when I installed MacOS Sonoma version 14.0 (23A344). The Spotlight and Search function on finder are working when I turn the computer on but after a while they don't work anymore. The same behavior with Outlook for Mac. When I restart the computer the same happens again. I tried to reindex via System Settings and Terminal but it doesn't fix the problem. It's very annoying to have to restart mi MacBook Air M1 every time I need to search for something. I remember when Mac OS Ventura was launched the same happened. Finally after one of the updates the problem was fixed. It seems that Apple launches new OS without verifying if all the functions are working well. Hope anyone can help me with this problem.