This is what I mean -- previously I built a similar search engine on top of slack, notion, etc., but didn't launch the product because I thought that requiring users to constantly add bots to private channels would be a subpar experience. I thought this would be a blocker for good UX, so didn't go further, but maybe you'll find a nice solution!
Searching over public internal data is addressed by a few existing tools, but it's the private aspect which is pretty difficult to handle and disastrous to get wrong when managed ad-hoc - e.g. someone accidentally adds the bot to a private slack group called #layoffs :) so you'd want this handled properly and centrally.
I guess you'll also need to handle privacy well, ~maybe it's OK when run as a SaaS for db admins to have access to ingested data, but if it's OSS then the people that run it probably shouldn't be able to read the private data that's ingested, so now you need to handle search over encrypted data, which is a fun problem :D