DataBinding Guide States
By default, a Binding class will be generated based on the name of the layout
file, converting it to Pascal case and suffixing “Bindi
What is your layout name?
The above layout file was activity_main.xml so the generate class was ActivityMainBinding.
What this means is that the generated class name will depend on your layout's name
activity_main.xml -> ActivityMainBinding.java
I think your activity name is "main_activity", so the generated binding class name should be MainActivityBinding not ActivityMainBinding