Incidental 8 years old

An old client has got back to me 8 years later with a site I designed with the theme Incidental - the php is 5.3 and when I tried to upload the site onto a server with the latest php it just crashed. I was wondering does anybody have an opinion about simply upgrading the theme now with the new version of Incidental?
thanks in advance…

You should open PHP error mode and upgrade old functions with PHP 8.x versions.

thanks AthenaStudio, got it sorted by just upgrading the version of Incidental - everything remained where it was except the menu disappeared. Got that back up and all good. Thanks for replying!