You can use creative mode to practice your runs and explore the map, but whenever you are recording a run and you want to submit it, you first have to open to LAN and enable cheats so that you can set your gamemode to 0 or 2. Those are the only acceptable modes for submitted runs.

Can you send the text written in the pack.mcmeta file? Also make sure you unzipped the pack and it's in a folder in the resourcepacks directory of .minecraft. This folder should have 3 items: a folder called assets, a file called pack.mcmeta, and an image called pack.png. If this is all in order, then I am not sure what the issue is.

Yes I already submitted a run for level 1 but idk how to do anything after that. I tried to find the command blocks that are controlling the timer but every time I went underground it kept tping me back to the start. So if anybody knows where the command blocks are I can work out a way to create a resetting timer for each checkpoint. Thank you for the response though.

I'm trying to run each level individually but how would I restart the timer for each section starting from the first checkpoint. Should I just use a timer like live split or is there a way to use the in game timer?