I am searching for something to sync my phone contacts between multiple phones for some time. Best case it shouldn't use DAVx^5 and should support Android and iOS. Thanks for your suggestions!
What I found so far:
Nextcloud - but needs DAVx^5
Radicale - also needs DAVx^5
SoGo - needs some CARD-DAV application
What's your problem with DAVx^5? It's completely and permanently free and fully-featured on f-droid. Only the PlayStore version costs money. The authors don't want to make money, but motivate you to move away from Google infrastructure.
If you only need address/phone number sync, then nextcloud is probably overkill, but I use it, and it works great. Also for calendar sync and file storage.
(You don't need to put the community name in the title, especially not with "@", which signifies usernames. Communities are prefixed by "!".)