Is it possible to set a global default for all trills such that there are displayed as tr + trill line only. Currently, I have to manually change each to Accidental - Hide / Appearance - Accidental in the check boxes in the lower panel.
I don’t find an option for that… What you could do if the option doesn’t exist is: select one trill, Ctrl+Shift+A several times until all your trills are selected, then activate Accidental > Hide in the properties panel.
(And set the Properties scope to “Globally” if you want to affect both score and parts.)
If you set the Engraving option to Accidental, then you will only see that accidental if the trill interval requires it (in which case an accidental IS required).