This addon can be used to pregen bedrock worlds while AFK
Add the behavior pack add-on to your world, start the world, then stand in the middle of the area you want to generate and run /function start#.
For example, if you are at 0,65,0, and you run /function start500, you would generate the whole area between -250,-250 and 250,250. All you have to do is AFK till it says it is done.