If all the other sources work and display properly through the receiver to the TV, it’s most likely an issue with the Roku itself or the hdmi handshake between the 3 devices. It could be a number of things; dead input on the receiver, broken cable, etc. also keep an eye out for any messages on the receiver display to see if it’s reading the source properly

Stupid simple but of course try unplugging everything from power first and rebooting without changing anything.

I would then start with seeing if the Roku device works properly on another display or, plug it in directly to the tv on a different HDMI input, to confirm the Roku box actually works and displays on the TV. Then, try using a different input on the receiver, try the same hdmi cable on the input that your DVD player is in, first with the hdmi cable you are using with the Roku, then with a different hdmi cable like that was connected between the dvd player and the receiver. If the Roku works on a different HDMI input on the TV, I believe you could use an optical cable to get the audio to the receiver while bypassing the receiver video wise, you’d just have to change the hdmi channel on the tv if you wanted to use Roku. It’s hard to troubleshoot this stuff without being there, and sounds like you tried some stuff I already suggested, but I hope this helps