Set the battery usage of your essential apps to Unrestricted and your persistence problem is solved

The background app battery usage feature (otherwise known as "allow background activity", "battery care", or "Adaptive battery") is a different feature to what I'm talking about here sadly AFAICT, and doesn't affect the relative importance weight of apps when Android's memory management is looking for things to kill.

The only thing that the background app battery usage restriction does is stop "inactive" apps from running in the background if they are using up a lot of CPU time, and if the app is not being interacted with frequently: either directly by the user, indirectly via Google Cloud Messaging, or by another app on the device. From what I can tell, it's completely separate to Android's memory management and solely exists to extend battery life.

Android has vastly improved its security by cutting off the workarounds shady (and legit) apps have used to persist.

Shady apps already persist using Google (Firebase) Cloud Messaging, and this change does not impact them. Even if they are killed by the separate background battery app usage feature, a simple push message typically brings these back.

The hacky workarounds you speak of to maintain persistence on A14 should be killed off to improve everyone's privacy.

I wouldn't exactly categorize this as a hacky workaround, since it follows the documented relative app importance weights used by Android's memory management. Users can even bypass this themselves by swiping on the persistent notification, and hiding those types of app notifications.

If anything IMO it forces apps to be less transparent about their activity, since they cannot communicate to the user that they are running

If I'm wrong about the background battery app feature's seemingly lack of impact on Android's memory management please do let me know - I've yet to come across anything suggesting it does ☹️