I've had the exact same issue with my A90 5G, seems to be a recurring theme.
I managed to get through to Samsung and they arranged a DPD pickup the next day. Good service so far. Not quite. Heard nothing at all from them after phone was picked up, then a random text a week later to say it would be delivered this afternoon. Unboxed what I hoped would be a fully functioning phone, but same issue. Black screen, vibrations on a soft reset and occasional vibrations when I assume an email or notification comes through. Has anyone had a positive resolution??