Write mode stops working (can't find 'Disable Condensing' option in Layout)

I am a newbie, playing around with note input. Things seemed to work well, but then all of a sudden, I couldn’t input notes any more. I remembered that before that happened, I clicked on the notation symbol at the lower-left corner (I really don’t know what the notation popup from that small panel is for.)

Edited:
Just now, I closed and reopened the project. Then Write mode works normally. Strange.

Edited:
I forgot to mention that I was in ‘Lead’ sheet. When I just now opened a new project in Piano, the write mode works normally.

According to the answer to another post, the problem might be that I accidentally enabled ‘Condensing mode.’ And according to Dorico help, I should be able to find Enable/Disable Condensing option in the Player section of Layout mode. But when I Cmd-Shift-L, I couldn’t find it there.

Simon,
in the Layout Options there is a search field at the top left, which will help you finding things.

Regarding condensing, please also have a look in your Edit Menu:

You can also enable/disable condensing by choosing Edit > Condensing.

If you are a beginner, I would make sure to have condensing disabled. It is a very complex mechanism and it will take time to understand how it works.