Roku does not create channels for third party providers. It's up to the providers to create and maintain channels for Roku devices.
Your Message title says Disney+, but your message says Discovery+. Both Disney and Discovery are available on Roku devices, but not in every country. Discovery has a Roku channel called Discovery Go. However, you need a TV provider subscription to access it, meaning a cable or satellite provider, or one of the online providers such as YouTube TV or Sling. However, you still might run into issues if you're not located in the US. If you are not in the US, you would need to contact Discovery themselves to find out if their programming is even available where you are located.
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.
