There are a few different ways to do it but what I have done is create a new splashscreen image specifically for Android 12, 436x436 px.
For the actual image I used my app icon centered in the middle of the splashscreen image, ensure plenty of space around the icon and the splashscreen image so it doesn’t get cropped on different screen sizes.
I named that image android12splash.png. I created a new folder in my project folder and named it “images” and put the new splashscreen image in that folder.
In Project Explorer side bar menu > “Project Properties and Global Code”, scroll down to “extraFiles” and enter images (this is so the images folder will be included in the build).