Page not suitable for mobiles | Maybe a solution

Hi, Since June 2021, I've run several tests on my website https://la-guitare-de-joe.fr in order to solve this problem : page not suitable for mobiles. First, I'v disabled AMP (accelerated mobile pages) to see if this Google Plug-in is the origin of the problem. But, apparently not. Secondly, I've run several test with WP Rocket and my theme Audioman Pro, and I think I've found the problem. It seems like when you want to minify CSS, the page become not responvive for mobile. Right now, I can't find the way to find a solution for that problem and I'm here to find if we can solve this minify CSS issue. Meanwhile, I'v installed an another them, so that I can keep my pages responsives. Best regards Joe