I've used PhotoPrism and Immich. Everyone's definition is different I have about 100k photos and videos which are a bit over 1 TiB (original data, not thumbnails and previews). Nether had any performance issues with a few minor exceptions on Immich (I don't recall anything from PhotoPrism but it has been a while now since I switched)

1. The Immich app's performance is awful. It is a well known problem and their current focus. I have pretty high confidence that it will be fixed within a few months. Web app is totally fine though.

2. Some background operations such as AI indexing, face detection and video conversion don't work gracefully when restarted from scratch. They all basically first delete all the old data, then start processing assets. So for many days (depending on your parallelism settings and server performance) you may be completely missing some assets from search or converted videos. But you only need to do this very rarely (change encoding settings and want to apply to the back catalog or switch AI search model). I don't upload at a particularly high rate but my sever can very easy handle the steady state.

1 is pretty major but being worked on and you can work around it by just opening the website. 2 is less important but I don't think there is any work on it.