Gather round, and I will sing you the Ballad of the Tenors.
The early versions of Dorico treated the Tenor as a transposing instrument, like a Contrabass, or a Piccolo – where the octave transposition is implied, but not explicitly stated. (There are, after all, plenty of scores where the Tenor part just has a standard G clef with no 8.)
Octave clefs were “cosmetic”, in that they didn’t affect the pitch: that was done in the instrument definition itself. (I believe Sibelius works the same way.)
There was “some debate” about this, and eventually, Dorico introduced three new features.
The first was the option for Octave Clefs to actually change the pitch of the music. You will find this in Notation Options > Clefs: “Respect the Octave”.
But of course, the Tenor instrument already transposes down an octave regardless, so if you respect the octave, you’ll be down two octaves!
So there are two Tenor instruments: one, down an octave, and the other at ‘normal’ pitch, for use with ‘working’ octave clefs.
Should that still not be sufficient, you can set the octave shift of any manually added clef.
So: in short, either use the transposing Tenor and “Ignore” octave clefs; or use the ‘normal pitch’ Tenor while “Respecting” the octave of the clef.