There are already DoTs I configured previously in my system. As I do not want my router to use Turk Telekom DNS servers (which are the DNS servers supplied by my ISS), I disabled the option "DNS servers supplied by internet connections" which totally broke my access to DoTs as well.
As a note, I had both DoHs and DoTs but after upgrading to 3.8 Alpha 1, all my DoHs have gone away and left with only DoTs.