By "Roku dongle" I assume you mean a Roku Stick, which connects directly to the HDMI port without a cable. The Stick has no external USB port, and does not support connecting a USB hub to the power port. That means you're connecting the USB stick directly to the Samsung TV via USB. So the second Roku is meaningless.
If you have one device (the Roku TV) that can play a video but another device (the Samsung) cannot, then the problem is with the Samsung. Since you are getting a message about formatting the drive, that indicates your USB drive is not formatted with a file system the TV recognizes.
- Roku supports the FAT16, FAT32, NTFS, Ext2, Ext3, exFAT, and HFS+ file systems
- Samsung QLED and SUHD TVs support FAT, exFAT, and NTFS file systems. Full HD TVs support NTFS (Read Only), FAT16 and FAT32.
You can see the lists don't match up, so your USB drive is likely formatted in a file system that Roku supports but Samsung does not.
Dan
Roku Community Streaming Expert
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