Hi there!
I have tried to replicate the issue on my site, but I am able to add a variable product with the latest version 9.7.1.
Also, I tried to access the link you shared, but I am getting a 403 Forbidden error.
If you are using any security plugin, could you please disable it temporarily so that I can access your site and try to replicate the issue on my end?
In the meantime, could you please check the browser console (Press F12 > Console tab) while trying to add the variable product to the cart? If any errors appear, please share them here so we can investigate further.
Also, I’d like to understand your site properly. Please share with us the necessary information below for us to investigate the issue further:
- System Status Report?which you can find via WooCommerce > Status
- Fatal error logs?(if any) under WooCommerce > Status > Logs.
Please use https://pastebin.com/ or https://gist.github.com/ and share a link to that paste in reply here. Once we have more information, we’ll be able to assist you further.