You are mistaking KMail (desktop client by KDE) and K-9 Mail (Android client that is being rebranded into Thunderbird for Android).
You are mistaking KMail (desktop client by KDE) and K-9 Mail (Android client that is being rebranded into Thunderbird for Android).
I especially appreciate that the graph is designed as “Linux” and “Other” instead of “Windows”, maybe “MacOS” and “Other”.