I just want to start over from scratch. But how?
I suggest creating a different Joplin profile and using a different Joplin Cloud account to experiment with a JEX backup of your full dataset.
I am able to sync 10k notes, 20k resources, 10GB in a few hours to JC. How many notes, resources and GB do you have? How many tags?
More suggestions: How to survive with a large dataset on Joplin (10k notes, 20k resources, 10GB)