VICTORY
I was also having this issue (Alfred file searching not working) after transferring my macos Monterey via their Migration Assistant. (Which in itself was a huge pain and Monterey is filled with bugs but ignoring that for now...)
Using the wonderful suggestions here, I was able to do this to solve the issue:
1. Switch to another user on the machine, play around with Alfred, then switch back and it magically works. (Per this post
)
2. Rebuild the index following instructions from this post