Same issue here as well. I have two Roku XS 3100Xs in my kid's rooms that I specifically purchased because they have and can play media from USB devices - but neither one of them will add the channel. My Ultra downstairs picked it up right after I added it on the My Roku website.
I'm hoping this is just some kind of rollout issue.
I found issues still. For one, the Star Wars splash screen isn't loading.
However, everything is fine on my Roku TCL TV.
I'm beginning to suspect the use of the MicroSD card.
I found this:
Not sure if your Roku device will have Disney Plus available at launch? Here’s every Roku model that will have Disney Plus:
I’ll also note that you need to have the latest version of Roku OS (version 9.2) in order to be able to install Disney Plus. So, if your device is no longer receiving Roku OS updates, you’ll definitely need to grab a newer Roku or pickup any of the other Disney Plus-ready devices.
Since my XS is a 3100x I guess it's not going to work. Would have been nice to know this a couple of weeks ago - Disney + was only announced more than 6 months ago
Based on several reports I've seen, Disney appears to still have a few issues to iron out with the channel. Give them a little time. I'm sure they were deluged with new users yesterday.
All of those old Roku devices (2 XS, 2 XD) are legacy players that are no longer supported. They won't get OS 9.2, therefore Disney+ won't work on them. Yep, time for an upgrade.