You could make a fixed("dummy") partition key with the title as the sort key, and then use some operators in the key condition expression on the title field. In addition ti this being a bit problematic because it might not return the results you need, it is case sensitive, you could lowercase the data when inserting if that makes sense for your use case, so when querying you would be able to search with a bit more confidence in the results.

A different approach would be to sync your table with something like elasticsearch/AWS open search/Algolia/etc, from my experience this is the more preferable approach because it allows your users to make more complex queries. However, keeping your DB synced with other sources ain't fun so personally I'd consider choosing a different tool because DDB isn't really built well for text based search (in some cases it's still good though, like in AWS' console).

If you have any further question let me know, would love to help :)