Proton Calendar

I am finding more and more businesses I am dealing with are sending me shared links from Proton calendars. There doesn't seem to be anyone in the space with a desktop app that can 2-way sync with Proton calendar. It might be something to consider to contact them about that and possibly become a first market mover on it. I have recently had to set up a Protonmail account for one of my businesses to receive and edit a shared Proton calendar.