LDD Broken with 4.21 and up?

I maintain the web site at https://www.idylwood.org. Before, the business directory had been working fine.

Now, the front page displays correctly, but when you click on a listing, it seems like some kind of transparent overlay pops up and nothing happens.

Plus, on the backend, you cannot add a listing or a category. When you fill out the forms for either a new listing or a new category, and hit SAVE, it goes to a 404 Page within the dashboard. Kind of odd. ANy ideas? We really want to use this plugin, and in fact, I am getting ready to need to use this or something quite similar on a new project. I will be happy to pay for troubleshooting. Thanks.

https://www.ads-software.com/plugins/ldd-business-directory/