Probably not going to be easy, but i believe it's possible.
I see that Android has a "Notification Listener" component, but i don't undertand if it can get all notifications, or only those posted by your application
If you have no experience i suggest you use one of those frameworks to build app, they remove a lot of the complexity in getting started, building layouts and entering into the mindset of the maniacs that created the official tools. Poor souls.
Plus, for anything that is not this platform specific you get multiplatform support.
Plus, they don't radically change every couple of years, when the maniacs that mantains the official tools change. Seriously, if you find a tutorial or course make sure it's from the previous two years or newer, or you won't be able to follow with the current tools.
The framework that i use is called "Basic 4 Android", it is really easy to get started, there are a lot of official libraries (unlike flutter which a few months ago still relied on "the community" for most libraries and libraries support, most libraries were junk. I tried five different BLE and each had problems that made it useless). The community is one of the best i've ever seen, the power users there are really knowledgeable and willing to help, and 99% of the time the first one to answer is going to be the creator of the project with just the words you were looking for. The documentation is always up to date.
What i suggest is that you pick one of these frameworks, and go by steps. Open one example project (a tutorial from the forum) and see how it's built. Start with your own application to get used to building the layout and making things work. Add the BLE component and connect to the BLE device and interact with it. Add the notification listener library/component and play with it, see how to change other applications notification settings (that's going to be the hardest part. I believe it's possible though)