As you know, there are several Mali Midgard directories in Samsung Galaxy's kernel source.
drwxrwxrwx@ 141 eee staff 4512 10 29 2020 b_r10p0
drwxrwxrwx@ 142 eee staff 4544 10 29 2020 b_r12p0
drwxrwxrwx@ 142 eee staff 4544 10 29 2020 b_r14p0
drwxrwxrwx@ 149 eee staff 4768 10 29 2020 b_r16p0
drwxrwxrwx@ 158 eee staff 5056 10 29 2020 b_r19p0
How to know which one is actually used in my device?
This will depend on the device. If you go to chrome://gpu in chrome on your device and scroll down, there will be "Driver Version" in a table. It will be eg 19.0.x rather than r19p0, but the first number will tell you which of the above it is.