In reply to Li-An.

Maybe the Advanced Editor Tools (Formerly TinyMCE Advanced) plugin might work for you. It has an option to open every post (or page) with the classic block by default.

Alternatively you can switch to the Classic Editor entirely. But this default Classic Block (default meaning you don’t have to select it every time, which is extra clicks) might be worth checking out. It adds TinyMCE extras as well.