You can back up your app first.
After that, open a copy of your app--> right click your app--> select Properties option
-- select Android Targets
on the left, then you can select the required net9.0 for the Target .NET Runtime.
After that, please build your app, then it will download the required Android dependences for your app(I did a test on my app, I need to build my app two times).
Then ,proceed with further actions based on other build prompt logs on the VS.