This is a big issue with Nostr. Google taught us how revolutionary a good search engine can be, we need to find out a solution at least for a "good enough" decentralized solution. Often users need to search for events they remember and need to recall in a limited timeframe, less than 30 days, so perhaps a local relay with NIP-50 is sufficient. But how many would use it? Once again, we face the delicate issue of having clients with a local database, that maybe as bonus can expose a local relay for other apps. Or we can develop a Nostr search engine, invite passionate users to setup it and have something like

Invidious Instances

where end users can pick their daily instance checking availability, features, spam policy, etc. Finally, I don't remember if @Kagi was considering opening its search engine as a NIP-50 relay to paying customers. It would be a great additional tool.