With the default search or only with my Scout extension?
The default Flarum limit should be infinite in theory, since the search keywords are just added to the existing SQL query.
The Scout extension on the other hand first retrieves the list of matching discussion IDs from the search driver, and then uses that list to build the Flarum SQL query. So there's no way to get past the number of pages that the search driver generates. But there's usually a way to change the number of results returned by the search driver, either on the search service server itself or through the implementation in the Scout extension.
Also of note with my Scout extension, there are 2 indexes for discussions and posts. Both need to have their limits raised to achieve a larger number of results (might be necessary for Meilisearch).