I moved all my movies on dropbox basic 2 TB - (NO business). It is working well, only folders are really slow.
I have different folders, with movies, kids movies, tv ect… When I go to movies, where I have about 300 movies (also in folders) Infuse spins and spins for about 1 min.
Then all files shows fine - if I go back and select movies again, I can wait 1 min. again. When i search for movie or use the find newest, it is also fast.
I use infuse on iOS 13 / iphone 11 and a ATV 3
I have setup iCloud sync
I have played with different settings - no changes