On every page you navigate to from within the website you'll first get a pop up asking to choose between browser and reddit app.
Or maybe I'm just getting old :D
The new UI is terrible and barely useable. But Gen-Z is used to barely useable UX. (looking at you, Snapchat)
Heyo that's awesome! I feel ten years younger.
There's a user setting for this, somewhere. I found it once. It's default on but once you un-check it you no longer see the app nags. It's great. And terrible they hid it like that.
--edit-- Or there was, damned if I can find it now.