Yes, Redmi 6 does have the 18:9 aspect ratio full-screen display.
Yes, you can play PUBG on Redmi 6.
Yes, Redmi 6 does have the 3.5mm headphone jack.
You can record up to 1080p resolution videos with Redmi 6.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.