A used phone. New budget phones are generally pretty bad, so I would recommend something like a Pixel 6/6a or a Galaxy S20/S21.

At this price point, I’d probably recommend either the Samsung Galaxy A23 or A14, or the Nokia G60 or G42.

€250 is a hard price point but a Samsung A series is probably going to give the best performance for the money.

The strongest OPPO you can find in your neighborhood.

My vote goes to the Realme 10 or one of the Motorola Edge. Both are really solid choices.