End-of-the-turn casting in Magic Arena
You can activate full control mode.

MTG arena has policies in place to speed up the gameplay considerably. This auto pass of priority is an attempt to remove the slow gameplay that has plagued MTGO.

You can deactivate this feature temporarily by pressing CTRL, you can turn it off permanently by pressing CTRL + SHIFT. Take note that when I say permanently, I mean for that game only; it will revert back to the default of setting when you start a new game.

Read more here.