I definitely see the frustration with fonts when switching between mobile/desktop platforms. It sounds like this may be due to Windows having explicit font settings (10,12,14 etc..) and iOS having implicit font settings (Small, Medium, Large). When switching between font sizes in these scenarios across each platform, it can sometimes lead to unexpected results.
While not ideal, a possible workaround would be to set your desired font size on Windows and to not change back and forth between Small, Medium, Large on iOS (keep it on the default while editing notes created on Windows), as this might sync back to Windows with an unexpected size.
If you're performing different actions or steps that cause the unexpected behavior you're seeing, please do let us know the exact steps you're taking and what you're seeing.
The development team is investigating how to more appropriately handle the size adjustments between clients in the future, but I don't have an estimate on when to expect this.