All the checks say successful but nothing ever syncs. I know my Radicale setup is working right because I am able to sync to Android via Davx5 and to my desktop via Thunderbird. I even setup Baikal as well because I read somewhere that it has iOS support, but ended up with the same issues. I can sync with Android and Desktop but not iOS.
I’m not sure if this is your exact problem but it’s worth investigating. I had to fix this before iOS clients started syncing with NextCloud. Desktop and android clients would sync fine.