Probably somewhat similar to how Trino/Presto/Bigtable/Spanner works but targeted at search, decompose the query into a set of highly parallelizable steps and execute them simultaneously over the set of data using some type of specialized storage format for rapidly indexing into the file, some really nice heuristics, and then drop all the ones without a potential for a hit, aggregate the rest and then do maybe a more classical search over the vastly reduced set of potential files in memory.

I know Presto isn't focused on search, but Athena (AWS branded Presto) can do some really fast queries over S3, the issue is coldstart time on the compute, for a similar solution focused on search maybe you keep the compute always warm and work from there.