How to Resolve Theme Compatibility and Plugin Conflicts After Latest WordPress Update?

Hello, I recently purchased a theme from Envato for my tool-based website, and after updating WordPress to the latest version, several key elements are malfunctioning. The site layout is misaligned, dynamic features like sliders and interactive forms have broken, and some widgets fail to load properly. I’ve already tried standard troubleshooting steps—clearing cache, disabling plugins one by one, and reverting custom CSS—but the issues persist. Additionally, I’m seeing new JavaScript errors in the console related to AJAX calls and deprecated functions, which weren’t there before the update. Has anyone encountered complex theme incompatibilities or plugin conflicts like this after a major WordPress update? What deeper-level fixes or debugging techniques can I use to resolve these issues and restore full functionality to my site?