Transposition in Dorico seems to be based on the premise that an entire piece (flow?) remains in a single key. (If I’m mistaken, I’m happy to be corrected.)
But if a piece has multiple sections with different key signatures, it seems one must transpose each section individually. I’m not talking about different flows; I mean the sort of thing where the middle 8 of your piece has such a different tonicization from the rest that accidentals are impractical. Or where the last chorus of the song is bumped up a whole step, etc.
Finale’s transposition tool offers a setting to transpose all keys proportionally (i.e., everything up a minor third, etc.–so the C major section would be bumped to Eb, the F# minor section would go to A minor, etc.). And it offers a “wrap keys” function, intelligent enough to realize there’s no such key signature called “B-sharp major” or “E-double-flat minor” and adjusts accordingly.
Please, for the sake of those of us who use multiple tonicizations, find a way to implement a similar function in Dorico.