Answer by Liyun Zhang - MSFT for How do I use a custom font?

As you see:

    // this is how you set the font according to samples      Font = Microsoft.Maui.Font.SystemFontOfSize(14)

And I have check the source code about the Microsoft.Maui.Font, the font family is read-only. So you can set it as a custom font.

In addition, I also checked the source code about the ios platform snackbar. There is no override method can custom it.

You can open a feature request on the CommunityToolkit/Maui repo.