Can't connect to my iMac - although it is shown "online"

Hi all!

I hve no more ideas what to do; I tried everything:

I want to reach my IMac from Mac Book Air (both TeamViewer 13)
The system show the iMac "online"
The energysaving mode has NOT activated the checkbox "password required" after screensaver mode

But if I wake up the iMac manually or better turn off the screensver manually, it works and I can connect to it

What can I set up, to be able to connect automatically?!
I also want to be able to connect automatically WITH set password in screensaver mode

Thx,

Nils