"USB drives can be formatted with different file systems. Roku devices support USB drives that are formatted with the FAT16, FAT32, NTFS, EXT2, EXT3, and HFS+ file systems. Many new USB drives are pre-formatted with the exFAT file system, which is not supported.
If you don’t know which file system is used, insert the USB drive into an available USB port on your computer. When the drive appears on the desktop, right click on the icon with your mouse and selectPropertieson your PC, orGet infoon your Mac." From this page.
EXT4 is unsupported by the Roku OS, so it's meaningless about what player might support it. Once your drive is using a supported file system, the Roku Media Player will play your media, assuming the media is in a supported container and uses supported codecs.
Your only other option is to connect the EXT4 drive to a computer that supports that FS and use DLNA to play the media from that computer to the Roku, again using RMP as the player.
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.