Apparent PHP Incompatibility

Gentlemen: I use your Catch Responsive Pro theme on my website https://www.puertoricobygps.com/ and I have a problem that’s driving me crazy. I can no longer access my custom CSS. When I go to “Appearance/Customize”, where I used to access my custom CSS, as well as all the other settings for Cache Responsive Pro, I get the following message: “There has been a critical error on this website. Please check your site admin email inbox for instructions. If you continue to have problems, please try the support forums. Learn more about troubleshooting WordPress.” I tried turning off my plugins, but the problem prevails. I’m running version 6.9.4 of Wordpress, PHP version 8.1 and Catch Responsive Pro 5.2.1 . I upgraded my theme on January 30, 2026 (Invoice 315229) . If I downgrade my PHP to 8.0 the problem goes away. But then, other software that I'm running stops working, because it requires PHP 8.1 or newer. So that brings me to the question: is the problem Catch Responsive Pro 5.2.1? I've been working on websites for a long time, so I've learned the hard way (by crashing into things). However, I'm hardly a techie and “quite frankly” I'm at the end of my rope. Can you help?