finally came around to read the f-droid blog post, play with UP and check its status at key projects. I encourage anyone read the WebPush section. UPs prior position on encryption will be loosened up by supporting rfc8291 of WebPush.
While Nextcloud has an app to be provider, Nextcloud itself doesn’t yet support pushing to a UP provider. Seems to me it’s more likely to arrive with supporting WebPush as it will benefit the browser usage at the same time (notifications when no NC Tab is open).
To check upon a project you care about (Signal, Telegram…), go to the wishlist, the issues link the external repo discussion of the project
As of now, no App I personally use can facilitate UP, mainly due to missing serverside support for pushing to an UP provider (it’s a chicken/egg problem). I mostly care about notifications for Calls, as they’re time critical.