How do I undo Control+Command+3 keyboard shortcut on Mac?

^-⌘-1 (control-command-1) also works to clear this.

Here’s the usual list: Mac keyboard shortcuts - Apple Support

But unfortunately*, that list omits ^-⌘-1 and ^-⌘-3 (and the other group-by choices), but Finder itself shows them.

*bug report logged

Click on the folder with them, open the Finder's View menu, and uncheck Use Stacks or Use Groups.

(264121)

1. Make Finder active with no Finder windows open (to apply it to the Desktop),
2. Show View Options (⌘J, or menu View﹥Show View Options),
3. Change “Stack By” (and optionally “Sort By”) to how you want it.