I couldn't reproduce the problem on my own test site, so I took a copy of your site to do some testing on, and it seems you are using an advance development release of elementor, and that causes the problem.
Switching to the current production release of Elementor the PHP errors do not occur.
I suggest you do not use development or beta versions of plugins on your production site and use then only for testing.
We don't debug compatibility issues with pre-release versions of 3rd-party plugins as the issues often disappear by the time they get to production.
Confirmed the same issue and rolling back to Elementor 3.4.8 solved the customizer issue, but now has standard plugin upgrade warnings that Elementor needs to be updgraded.
It seems like Elementor 3.5.0 is officially released but causes the error with Toolset.
@all please see this erratum for more details, which includes a patch to fix the issue until a full update is published.
(Note that there is a Types release expectedly imminently, possibly later today, and it does not include this fix, so the patch would need to be re-applied after updating Types.)