Hello,
My movies and series are on a big external HD connected to my Mac.
I access them with my Apple TV 4K.
What is the best or fastest format for the HD, APFS or ExFat for INFUSE ?
I already know the differences between the two for the Mac.
Thank you 
Pretty hard question to answer, but specifically for Infuse from tests that I’ve done APFS is the winner. The real question would normal be HFS+ vs APFS, and in those tests APFS reads faster (better for Infuse) while HFS+ writes faster. exFAT is slower than both, but it allows you the option of moving the drive between Mac and Windows.
Thank you, it’s all I needed to know 