In addition, apps schedule background work through WorkManager or JobScheduler or AlarmManager. Those can wake the app up at specific times designated to do this work. E.g. every X minutes when the screen is off.
Android has never had the same application execution model as traditional OSes. Both for foreground and background work. This allows it to scale multitasking with the available resources, mostly RAM, without losing app/user data. In other words Android can work on a 512MB RAM device or 8GB device and the only obvious difference would be how many apps are kept in memory. No data will be lost in either case due to apps getting evicted out of RAM. I typically give a 3-hour lecture to my interns on this because they need to know the details but that’s what it boils down to. 😂