I’ve remember that I have another Owncloud server (via openmailbox.org), so I upload there my calendar, synchronize it, added a new event at my phone and then it was reflected at the server so you are OK that Davdroid works fine and it’s something at my end.
Probably the problem was that in my server there is an Owncloud 5 old version while the one in openmailbox.org it’s 7.
While also noted that when creating Davdroid account at the phone it ask for an account name and it suggest for use an email account. First time I just give a no email account but just a word like “myaccount” and now I fill it with an email like “firstname.lastname@example.org”.
It’s necessary that account name must be a real email account?