-apple-system font, cant change it and it is causing 400 not found error

Hi, I got a major problem with the current version of NicePage. When I inspect the page on Chrome, I get a code error 400, pointing that the font "-apple-system" does not exist, firefox pointing to "The resource from “https://fonts.googleapis.com/css?family=-apple-system” was blocked due to MIME type (“text/html”) mismatch (X-Content-Type-Options: nosniff)."
I tried changing the font via the font system of Nicepage, but every time I change the font, it won't save the changes, so I can't change the "Theme Fonts" to anything else.

Please fix this issue as this seems to might be a security issue also.
Thank you!