Quick search in NAS. Which software for overview?
This solution is vexing and hard to solve generally.
We have had great success with one product and have tried many, none seem to work well as they don’t solve the remote index and then share that index out nail on the head.

https://cdfinder.de/

The marketing calls it the holy grail of media asset management, and I think that’s a little bit of an understatement. It does more than just that, it scales and is extensible and you can automate on top of it.
As you mention, the indexing would have to run on naps to be perpetually up to date, but periodic index scans by NeoFinder work well for us.