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 "!".)
Because Davx5 only works with Android and he stated he wants something that syncs across all of his devices. I came across this posting because I am also looking for a solution to sync contacts between my Android and iPhone. I am trying to get away from Nextcloud because it's overkill for my use case... So far I have tried Radicale and Baikal but neither works for iOS.
I've used Nextcloud and DAVx5 for years (back when X5 was still called DAVDroid). Works great.
That works for me since I use Nextcloud for other things. If you want to sync just contacts and calendars, I'd go with Radicale as I used that successfully before implementing Nextcloud.
Doesn't SoGo use Activesync? This wouldn't need an app on your phone.
I tried the same setup as you a few years ago. It worked, but I didn't like SoGo for email so moved to Nextcloud/SnappyMail and DAVx/K9 on my phone. Have been using this fine since.