Create "SYSTEM BREAK" in Write mode

Is there a way to create “SYSTEM BREAK” in Write mode?
I know in Engrave mode “SYSTEM BREAK” can be inserted by typing Shift-S, but this key sequence doesn’t work in Write mode.

I’m afraid not. The reason for this is a little technical (a system break is technically only created with reference to a specific music frame within a specific chain of music frames, which you can only address in Engrave mode).

I under your reason…
Why I ask… because I’m entering music from printed scores and I format Dorico to display in exactly the same layout (i.e. no. of bars in each staff line) as the printed score so that I can type in easily without missing any notes. This requires me to create SYSTEM BREAK for each line of music, which is why I ask for this feature. Or is there any feature in Write mode that can allow me to do this change in layout without invoking the Engrave mode?
Anyway, the SYSTEM BREAK symbol can be seen in Write mode and it can also be deleted in Write mode (this is a very good feature! Pls keep it.). It just can’t be created in Write mode.

BTW, after typing in music into Dorico for more than 2 weeks, I find that entering music in Dorico is much faster than in Sibelius!

You could set up the score layout of a whole page in engrave mode first and after that start with the music copying in write mode, that is how I do it.

Another issue I found with SYSTEM BREAK is that when I select the whole bar that has the SYSTEM BREAK (i.e. it must be the first bar on the staff line), the SYSTEM BREAK object is always selected along the way. If I paste it elsewhere, the SYSTEM BREAK is also pasted there, this is not desired. Is there a way to just select everything in this first bar without the SYSTEM BREAK object? It is quite natural that when a bar is selected for copying, everything should be copied but the SYSTEM BREAK.
(of course the present behaviour is not a showstopper since I can paste and simply delete the SYSTEM BREAK. I’m just thinking that this part could be improved to make work flow more streamline.)

Signposts are only selected when they are visible. If you exclude System Breaks (and/or Frame Breaks) in View>Signposts, this won’ happen anymore.