I was looking to replace my current application and use cryptomator. I was going to buy a license via Windows to support the project, and then realized I should check to see if there was an iOS app since I access my items via mobile as well.
When I went to the app store there it is $8.99 for the app. Thus as a user would have needed to pay twice to get features they have in other applications. This is also a sub-optimal user experience. Pay for the desktop app but also then each phone app; where-as a phone user only paid for the phone app first and will not be inclined to pay for the desktop app. It would feel more balanced to charge a one price to access all premium features; plus cryptomator would not be leaving ~$6 on the table for phone only users (Desktop is $15).
In this way a license is not simply Dark Mode but also access to the mobile apps. This would still support the spirit of free open source, but also cover expenses.