No. Redmi 6A does not have the front camera flash.
Yes, you can play PUBG on Redmi 6A.
No. Redmi 6A does not have Dolby Digital sound support.
The Redmi 6A is a fairly good update to the Redmi 5A, which itself was barely any different compared to the Redmi 4A. You now get a tall screen, better processor, and improved polish overall.