no.
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“Guaranteed End-to-End-Encryption” (the term we use for “Secure join”) is not limited to mobile devices. “Guaranteed End-to-End-Encryption” is supported by Delta Chat Desktop as well as Delta Chat iOS and Delta Chat Android.
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it is not needed that all devices have a camera. if you want to scan a QR code, you need a camera only one one device.
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if you do not have a camera on any devices, you can relay the needed information via an “invite link”
so, all you need is Delta Chat - in theory, other apps could add support for “Guaranteed End-to-End-Encryption” as well, however, we do not hold our breath right now 
a general note to understand priorities, (repeated from somewhere else ) Delta Chat does not consider PGP in its classic dealing-with-keys form as a convenient-enough approach to exchange keys or to guarantee things. we do not want users to be confronted with key questions in the UI they “reach”, Don’t ask users anything about keys, ever. therefore, effort and focus is put to other parts - autocrypt, secure-join, vcards etc. - resulting in far more messages being encrypted than on most other email apps