That command is definitely in 26 - you may need to check your menus in the Work Environment.
You may not be using a standard WE, in which case you will need to add the command or switch to a standard WE.
I am not a curtain wall expert.
It seems you can have a common frame at the corner (you can even make the frame invisible).
But it seems the panel can not mitre.
Unless someone can show us how to do it.
I am assuming it is a butt-glazed connection you are after?
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10