The sheet that I’m transcribing uses a single square notehead bracket to specify that two notes should be played with the same finger.
Is this supported? I always end up with a pair of brackets. I don’t see such a use case in the official documentation either.
Sure, the musical concept as such is not supported as an item but you can achieve this with a vertical line:
When you add the line with hooks, use Engrave Mode to adjust the length.
Just read up on lines.
I use the shift O, nonarp thing to achieve such marking. I’d say it’s supported for quite a very long time 
What is a ‘nonarp’ thing? I am not familiar with that.
Thanks all! Never knew. That should answer the OP satisfactorily.
It’s philosophically amusing that a non-arpeggio sign is classed as an arpeggio sign. 
It’s in the Ornaments panel on the right too.
Looks like both vertical lines and non-arpeggio signs work for my use case, and are near-identical in appearance. I personally prefer the former for this situation 'cause the latter feels like a misuse lol.
Thanks, everyone!
