Yes, Samsung Galaxy J4 does have the 3.5 mm headphone jack.
Yes, Samsung Galaxy J4 does have the OTG support.
No. You cannot record 4K videos with Samsung Galaxy J4. You can record videos up to Full HD resolution. It has a 13MP rear camera.
No. Samsung Galaxy J4 does not have the hybrid sim slot. It does have 2 sim slot and a dedicated MicroSD card slot. You can use MicroSD card of up to 256GB capacity.
Yes, Samsung Galaxy J4 does have the front camera flash.
Very Nice Display And Overall A Good Phone
The display is very nice. It beats almost all phones while using under direct sunlight. It has lot of other features also like power saving mode, front camera flash, etc.
I suggest this phone.