It is recommended not to store more than 100.000 files per library. This is the official recommendation and it is independent of the client.
As I said above: Seafile does not know a hard limit. I’ve seen libraries with close to a million files which didn’t cause any trouble. But there is no guarantee that it stays this way and the moment you experience problems, I’d tell you: Tough luck.
My recommendation: Do not even try to store 1M files in a library. Think about ways how to break up your data in a smart way. Based on experience, this is usually not so hard. You’ll be rewarded with a Seafile Server that is very stable and reliable.