how to make a block that normally is transparent but when a player gets near it becomes visible

you could make a transparent version of the block and when the player gets close swap it with the non transparent version and vise-versa

Create two blocks that have the same properties, including a tick rate of 5 ticks or less, but with one of them set as a transparent cutout block with a blank texture (1x1 with nothing in it) and the other one set to whatever texture you want. For the invisible one, have it run a procedure on block tick update that checks if there is a player within 32 blocks, and if so, replaces it with the visible one. For the visible one, have it run a procedure on block tick update that checks if not there is a player within 32 blocks, then replace it with the invisible one. (the strange formatting of not is intentional because that is how it looks in the procedure editor) if you need more advice, I would recommend that you search for some basic MCreator tutorials.