Instrument transpositions indicate the interval between the note an instrument plays and the sounding note produced. Transposing instruments, such as Horn in F and Clarinet in B♭, are commonly shown with their transposition, also known as their “instrument pitch”, as part of their instrument name or layout name.
Depending on the options set for Show transposition in the Edit Instrument Names dialog for each transposing instrument, they might show transpositions in staff labels even if you have hidden transpositions in staff labels in their layout.
Dorico Pro sets common transposing instruments, such as Clarinet in B♭ and Trumpet in B♭, to follow your per-layout settings for hiding/showing instrument transpositions in staff labels.
To reduce the risk of confusion, uncommon transposing instruments, such as Clarinet in A or Trumpet in E, are set to show their transposition in staff labels always, even if you have hidden instrument transpositions in the layout.