Ok, mates, I did it - I managed to revive this A510F with
A510FXXU3BPIB_A510FTEF3BPI5.
I had some issues though - the flash process again stops (without those red lines, that indicates downgrading), but this time at hidden.img..., so I had to remove this part from the flash file and voila - everything was fine. The phone is alive now.
@souloxo, you can find yours here
https://samsung-firmware.org/model/SM-A510F/page/1