The 'Request a Feature' link in the Calendar tab of Proton Mail for desktop goes to:

https://protonmail.uservoice.com/forums/932842-proton-calendar

Since the Calendar UserVoice forum has been merged with Mail, the link no longer works. Currently it this URL goes to the Lumo feedback forum. It should go to:

https://protonmail.uservoice.com/forums/284483-proton-mail-calendar

Proton Mail (macOS Version 1.10.1 (1.10.1))

Steps to reproduce:
1. Click on calendar tab
2. Click on profile image
3. Click 'Help and Feedback'
4. Click 'Request a feature'