We're aware of the issue and are currently gathering more information regarding this matter.
Meanwhile, you can do the following to resolve the issue:
The font displayed on mobile for product options is currently taken from your site’s Paragraph 2 style instead of from your design selections.
To fix this, you can edit the Paragraph 2 style in the theme manager.
This article is credited to the Wix team - https://support.wix.com/ and we thank them for that!