upgrade from 1.5 to 3.3.1 breaks website

I have recently taken over support on a website that has old plugins etc installed and i have been upgrading them but when i try and upgrade elementor it breaks the site completely returning 500 errors and all sorts of problems with the home page of the site not loading at all.

the site has a lot of plugins and is using the Genesis framework and theme

can anyone help identify how I can get this safely upgrade please

debug logging didnt give away any clues as to the cause of the issue