It sounds like you are trying to use the auto upgrader here. Thats not going to work, as you need PHP 8 for the latest release, and you are far enough behind not to be able to use it on your current version. You need to upload a fresh set of files from your client area (after switching to PHP 8 and ensuring all requirements are present), and run the upgrader from /admin/upgrade
If you believe thats what you have already done, I need you to leave that in place so we can take a look.