Am I missing something? I want it that way because that’s how we guitarist read music in other tunings (at least in Eb tuning)… :'D
(Also because the tab canged the music is sounding half step above and not half step below )
AFAIK Dorico does not handle scordatura (It would be nice if it did). When you retune the guitar, Dorico will adjust the tab to play the correct note (in your case the correct note is still A as far as the score is concerned). There are some clever folks here who could work out the correct transposition settings for you.
Internally, Dorico stores everything in concert pitch (sounding pitch) form, so by entering all the notes and then changing the tuning, you’ve ended with all the notes a step too high.
First you need to transpose all the notes and key signatures down. You can do this in Write > Transpose, where you want to transpose down by an augmented unison. This will correct the playback and the tab.
It will move the notation down, though, so you now need to ensure the guitar has a transposition that will move the notation back up. In the “Edit Strings and Tuning” dialog, under “Capo and Transposition”, you want to set “In staff notation, written C4 sounds as” to “Cb3”. Then go to Layout Options, and in the layouts where you want to show the transposed notation, tick the box that says “Use fretted instrument transposition” and set it to “For notation and main chord symbols”. Also ensure that “Transposing layout” is turned on for those layouts.