Borderlock

Borderlock is a game mode in which the world border is set to 1 block, and the radius increases by 1 block each ingame day.

You can either put the datapack inside the world before you generate it, or you put it in afterwards, but then you have to /reload.

Both available versions will work in either version, I just made it so that when you load the datapack it will not be marked as outdated.

If you don't want to start with just 1 Block and basically wait the first 20 minutes before starting to do something, you can use this command: "/worldborder add 2". I recommend increasing it by even numbers because this way it will always end on the edge of a block.