It'll vary depending on what phone you have but for mine I opened the phone's settings > apps and notifications > unified remote > app notifications and turn off 'keep Alice's, this should only disable the notification, not the feature in the app. If you don't use quick actions you can disable all notifications here.
I had this issue for ages too but seem to have gotten past it. Not sure what exactly helped but I tried clearing the cache ( in 'status' in the menu), that broke my widget so I deleted it and made a new one (from scratch) and seems to be working even with the app closed now. I've also disabled battery optimisation for the app and restarted the phone during this process. At some point my 'basic input' remote changed during this too, added buttons and slider bars I didn't have before.
Android 8.1.0 on a Nokia 8 (Pure android)
App version 3.12.0