How to add an iCal Calendar on Android (Fossify Calendar, DAVx5)? SOLVED

cross-posted from: https://slrpnk.net/post/36195475

I am trying to add a calendar in iCal format to my phone.

Fossify Calendar is nice and fully offline, using DAVx5 as sync adapter.

The link looks like

https://example.com/cal/export/5o2b2j393b21owbd829273b3

In DAVx5 I can only add an account, which does not work for this link. The only direct link to add is a WebDAV filesystem mount