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
https://api.invidious.io where end users can pick their daily instance checking availability, features, spam policy, etc.
Finally, I don't remember if nostr:npub1xsgymm0ne3vndqpvsvy285qfpu59049t5n5twg9vetmt92cyn95snyzazx was considering opening its search engine as a NIP-50 relay to paying customers. It would be a great additional tool.
nostr:nevent1qvzqqqqqqypzqmn477tj8972x227pax2p77xawwv0xlgtwha644ax7pzpj5wae6wqythwumn8ghj7un9d3shjtnwdaehgu3wvfskuep0qythwumn8ghj7un9d3shjtnswf5k6ctv9ehx2ap0qqsynhne9jtv0fzrw3hupqyqm5we83dmty6k7rrvpcm7ftlszawejdckwklhz