Expo detached android app deep link getting error "This URL doesn't map to any Activity"

I have a fully-functional expo project and I recently ejected it. It is using ExpoKit 36.0.0.

I'm trying to add deep link to the android app, which I'm using App Links Assistant in the Android Studio to add.

After I added an entry in URL Mapping and tried to check URL Mapping, it shows error "This URL doesn't map to any Activity"(I did put MainActivity in URL Mapping and MainActivity class exists). screenshot

I went on to do the second step "Add logic to handle the intent" and I selected .MainActivity(app), but it shows error "Can't insert code, because there is no onCreate method defined in your activity class."screenshot

Should I just add a onCreate method then? How should I write that method so it doesn't affect running normal expo stuff? Sorry if it's not a smart question but I have absolutely no experience whatsoever with android app development.