I have:
Apache/2.4.46 (Win64) OpenSSL/1.1.1h PHP/8.0.0 Server at localhost Port 80

I copied the osclass file and started loading osclass, but it gives me the error below:

Fatal error: Uncaught Error: Call to undefined function get_magic_quotes_gpc() in C:\xampp\htdocs\oc-includes\osclass\helpers\hErrors.php:74 Stack trace: #0 C:\xampp\htdocs\oc-includes\osclass\helpers\hErrors.php(104): getErrorParam('HTTP_HOST') #1 C:\xampp\htdocs\oc-load.php(84): osc_get_absolute_url() #2 C:\xampp\htdocs\index.php(21): require_once('C:\\xampp\\htdocs...') #3 {main} thrown in C:\xampp\htdocs\oc-includes\osclass\helpers\hErrors.php on line 74

Why can't i install oscalss on the local host?

Use php 7.x
Osclass 4.3.0 will support PHP 8.0 as well, but there is much more to edit.