It looks like the “required” attribute isn’t being inserted into the code on the page, not sure why, Lucas will know.
As a quick and dirty fix drop an HTML stack into the form in the location you want the checkbox and put the following into it…
It seems to work, although it’s not very elegant!
One of my other businesses/services is all about GDPR, I studied the regs, and actually read them, several times. I didn’t do what most “experts” did, which was read a few online overviews and take everything said as correct. Most of these overviews are written by people who scanned the regs at best, and assumed the rest.