I have 2 Roku 4661R devices, and I am wondering if via the USB port it will support devices formatted with the APFS File System. I have been using devices formatted with the HFS+ File System, but I am using the latest version of the Mac OS (Mojave), which uses the APFS File System.
Roku Media Player supports drives that are formatted with the FAT16, FAT32, NTFS, EXT2, EXT3, and HFS+ file systems. You can also access different partitions on the USB drive.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
I also have 2 of those Roku Ultra devices, and also for my 2 Macs, run the latest version of Catalina, which requires the device/partition it is running on to be formatted as APFS. But other devices, partitions, etc, can be formatted as HFS+, EXFat, etc. Of course the preferable "other one" is HFS+.
I have 3 Samsung external SSDs. All 3 have 3 partitions. 2 of them have 2 partitions formatted as APFS for my SuperDuper! backups, and the third partition is formatted as HFS+, and it contains various files, folders, etc., including movies and TV series. The third SSD contains an APFS partition for (future) Big Sur testing, and 2 other partitions formatted as HFS+, one containing a lot of movies, and the other containing a lot of YV series. For any of those SSDs, via a USB connector plugged into either Roku Ultra, I can watch a movie or a TV series contained on those HFS+ partitions.