Magento – Issue with upgrading Magento 2 from 2.3.5-p2 to 2.3.6

I had the same problem.

After searching the source of Magento 2.2.4 I found the function in file (vendor\magento\module-catalog-inventory\Model\Configuration.php):

public function getDefaultScopeId()
{
    // TODO: should be fixed in MAGETWO-46043
    // "0" is id of admin website, which is used in backed during save entity
    return 0;
}

In my case I modify Store parameters at "Stores > All Stores" and my actual store_id/scope_id was 1 and not 0. After changing "return 0" to "return 1", my problem was solved.

As this is anyhow TODO for Magento I expect, that in next upgrade this will be solved and all my modification will be overwritten and everything should work at that time...

I found a workaround for Windows OS. Image Adapter try opens to image files ('open function in Gd2.php line 63). validateURLScheme function return false always because it checking 'URL' format but local files not valid for this format, so it returns false.

Find validateURLScheme function in vendor\magento\framework\Image\Adapter\Gd2.php file. at line 96. Replace function with this:

private function validateURLScheme(string $filename) : bool   {
          $allowed_schemes = ['ftp', 'ftps', 'http', 'https'];
          $url = parse_url($filename);
          if ($url && isset($url['scheme']) && !in_array($url['scheme'], $allowed_schemes) && !file_exists($filename)) {
              return false;
          }

          return true;   
}