Hello, this is really FAR more difficult task than you think.
To your statements:
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I am not sure, where you’ve gotten these data
Based on StatCounter (Operating system/Windows share (December 2023) | Born's Tech and Windows World), the market share on desktop is 73% Windows, 16% macOS and 4% Linux.
And typically these are users that are not use to pay for any kind of software as they use opensource and free products only. -
Avalonia will not help us at all. It would mean to start UI development from the scratch. Please note, that eM Client is not based on WPF, but Windows Forms.