I got this error when I was trying to add an image to a manual nav block and I can’t go out of that page to undo the changes. I also don’t know how can I resolve the error bc that page is all I have. I don’t have access to the files, I was just editing the Atomik theme with the builder.
That issue is from using PHP 8 with something not compatible. You would have to either fix the code or update it ot switch to PHP 7. In any case you’ll need server access
That depends on your web host. Most web hosts provide an online access you can login to called cPanel. For details, see your web host’s help pages or contact your web host’s support desk.