When I try to install new locations, I have error:

Fatal error: Uncaught TypeError: count(): Argument #1 ($value) must be of type Countable|array, string given.

And many other errors:

Warning:  Undefined array key "action" in \osclass\oc-admin\locations.php on line 28
Warning:  Undefined array key "host" in \osclass\oc-includes\osclass\utils.php on line 979
Warning:  Trying to access array offset on value of type null in \osclass\oc-admin\locations.php on line 524
Warning:  foreach() argument must be of type array|object, null given in \osclass\oc-admin\locations.php on line 527

In PHP 7 everything works, in PHP 8 these errors.

I thought that the OSCLASS not works under php8 but then I read:

IMPORTANT: Osclass now fully supports PHP 8.1 version.
IMPORTANT: Osclass now fully supports PHP 8.2 version.

I checked under Linux and under Windows, everything is the same.

Thank you all, the problem has been found - cURL must be enabled. Although the osclass does not check this during installation!

Thanks for feedback.