“Whenever I like to work in gallery view and type ongoing notes, melodies etc. Dorico shows me multirests for the rest of the score, making it impossible to inserting new material.”
You can still add music with multi-rests turned on. Just use the arrow key to advance to the very start of the multi-rest measure and go to it. (Try it, you may like it)! But it is also possible to turn multi-rests off for any layout. And you can do this to many layouts at once by having them all selected before engaging the option. Full Score Gallery view will not show multi-measure rests, but the parts can be independently set to show or not show in either Galley or Page view.
If you are adding music to the end of a flow in which there are empty measures (like in your example), you will see a multi-bar tacet al fine, or the traditional bar count multi-rest (configurable in Engraving Options - Rests), but you can still add music to this multi-bar section as described above. As you do so, measures will be drawn to accommodate the music as you go. It feels a little strange at first… then liberating!
It sounds like your feature request is that Dorico could include an option to have just empty bars show at the end of a flow that is not a Full Score layout, as I don’t believe that’s possible now.
I hope this helps!