Fastmail does support the CalDAV standard, but calendly does not: https://help.calendly.com/hc/en-us/community/posts/245299227...
That’s entirely calendly’s fault.
Re:Mozilla VPN
by michaelbuckbee on Friday June 19, 2020 @12:42PM
(#23576137)
I _completely_ agree with you - but it leaves me in the same spot either way as I've yet to find a Calendly competitor that will work with CalDAV.
An open spec is great, but it has to be adopted to be used.
Isn't it down to the app to support those standards?