Hi,
I've never seen a request like this. I don't think it's a problem with MediaWiki. Can you give us steps to reproduce?

Hi @Zoranzoki21 I wanted to upload this file: [[en:File:Kuwait Petroleum Corporation Logo.svg]] by API but I get this error:

{"error":{"code":"verification-error","info":"File extension \".svg\" does not match the detected MIME type of the file (image/png).","details":["filetype-mime-mismatch","svg","image/png"],"*":"See https://ar.wikipedia.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes."},"servedby":"mw1222"}

How you wanted to uploaded file? How by API? Via browser or?

What is possible (steps):

1. Go on https://en.wikipedia.org/wiki/File:Kuwait_Petroleum_Corporation_Logo.svg
2. Right click and click on Open image in new tab (Chrome)
3. Copy URL https://upload.wikimedia.org/wikipedia/en/thumb/8/8d/Kuwait_Petroleum_Corporation_Logo.svg/418px-Kuwait_Petroleum_Corporation_Logo.svg.png
4. Try to upload via API

Looks like this is reason for error. And it is expected, because URL is to png file.

Given that the file could be uploaded to Commons, which sends it through the exact same checks, this is probably user error. (Although I guess the mimetype testing code could have changed since it has been uploaded, but it seems very unlikely.)