So many platformers on Scratch have the same method: Saving them as lists, which often ends up in obnoxiously long level codes. My system is simple: Place the blocks individually in the project itself. This is the most advanced thing I'm gonna work on yet. However, for larger levels, this will definitely not work, as I haven't implemented unloading and reloading yet. For large levels, I recommend Turbowarp. The next step is to spawn objects, which will hopefully be easier now that we have scrolling code.
Update 5/27/2025: Good news, player code! Bad news, bad player code... SO MANY Thanks to @IloveRoblox003 for helping me with the Tile Scrolling. Go follow them now or face the consequences.