Hacker News Reader

Data point: Spotlight and the Gmail app searches work great for me. What issues are you seeing?

Have you tried rebuilding your Spotlight index? https://support.apple.com/en-us/HT201716

Email search using the Gmail app on mobile works for you? That's a surprise to me, what is your setup? iPhone/Android, Download all emails / 90 days?

I did rebuild my index, I have a 1TB SSD drive and even excluded external drives.