After your watchlist is created, with potentially hundreds of items, there is no way to filter the watchlist for items available on your server. There is an ‘available on your services’ option, but it filters for only your streaming services. If I have 200 items on my watchlist and 20 of them are on my server, I cannot filter the watchlist to see these 20 items.
I suggest, at the least, adding the option to filter for your server’s content or add your server to the ‘available on your services’ option. When me and my wife want to scan through our watchlist to see what we want to watch, not having my own movies visible when filtering seems like an oversight. If I have Netflix, ATV, and movies on my server, I would like to see all of them on one nice grid.