Prowlarr, and if you want a friendly interface, you can try Jellyseer?

If you can host a docker container, have a look at Jackett. You can add tons of trackers, private and public and search all at once.

qBittorrent has a search function with many plugins already added and you can download more

Definitely go for prowlarr. you select the indexers you want to search through when you set it up the first time and then you just search for whatever you’re looking for in the searchbar and prowlarr will look through all the indexers you’ve selected and give you the result.