How to extract stock apk from TWRP backup?
Rename the system.ext4.win file to system.ext4.tarand extract it.
If your
TWRP backup is not in compression method, you will directly get to the /system folder or if your TWRP backup is in compression method, you will get a file named system.ext4 which you'll have to just rename it to system.ext4.tar and extract it to /system folder