Converted fonts (Bitmaps on protopie) that we view on mobile phones has crisp anti-aliasing as if there is a resolution problem. Normally on XD there is no problem. But when we import into Protopie & view on mobile there are crisp antialiasing problems on font graphics.
I think what you’re seeing may be due to the font not being installed on the mobile app. For this, the font license will let you know if this supported and how to do so. One possible workaround is to publish the prototype and view on assets.adobe.com.
Hope this helps!