This is the case. If you buy it via Google Play, you can edit or end your subscription via Google Play. If you did not, you need to use the desktop app to manage your subscription.
Ehh, I'm sure it's something like if they let you manage your subscription through the play store, Google is entitled to their 30% cut. If you subscribe through desktop, they'd like to keep 100% of the money opposed to 70%. Might be off base, but I'd wager that's the reason
I could've sworn this practice was recently outlawed? If not, it 100% should be. If you can buy a subscription from one location, you should be able to cancel it from the same location. I feel like I remember reading about a case recently regarding notoriously hard-to-cancel gym memberships resulting in a requirement that you could cancel subscriptions whenever and wherever you wanted, but maybe I'm misremembering.
Completely understandable problem, same for me where I have managed to move some smaller part of my community to xmpp but most would want to move to matrix.
With the way things are in my communitty I will prob just selfhost matrix server just to see how it goes.
That's the wonderful thing about the free market. You can cancel your subscription to discord nitro at any time and there's nothing they can do about it. That's all you have to do. Just cancel it then. You'll never have to worry about whether or not you can manage anything from the app because you won't need to. Isn't it amazing what you could do with your brain and your own money?