Following your link I found https://github.com/owncloud/calendar/issues/1002 and the second comment has a solution that fixes the problem for me. I did a vimdiff on his file and without understanding much I can tell you that the changes look reasonable. I have only been testing for 5 minutes but so far it works.
iCloud shared calendar - Impossible to sync
Motorola One Action
Android Pie 9 (PSB29.39-49-7)
DAVx5 version 2.6.2-gplay (321) compiled 12/22/2019
I’m using the application to sync my icloud account.
I have used “Connexion with an url and user name” for the URL : https://icloud. com and for the password I have generated a application password because of the iCloud’s double authentification
Some CALDAV are OK but for the shared calendar all is blocked : near the name I have an attention sign. When i check the box to sync it nothing happend.
Can you provide me some help.
Thanks in advance