Despite the greatest care, a technical problem may occur from time to time. If, for example, the download does not work immediately, this may be due to the mail provider. At Proton, we have found in the past that simply clicking on the download link is not enough.
The solution: right-click the download link and open it in a new tab. After that, the download will work.
If you notice any other technical finesse, feel free to let me know so I can record it here. In this way, you help others fix problems before they arise.