The function org-insert-structure-template is bound to C-c C-,. I can confirm that when search that function via M-x and seeing the shortcut behind the function name.
But I use Emacs (from Debian 11) in an SSH terminal (on Windows 10).
The second part (C-,) has no effect. A assume it is suppresed or interpreted different from the SSH terminal.
Any suggestions how to deal with it and how to deeper diagnose this?