@Ryan1729 good on you for trying.
One thought on why it does nothing is that something has to do the selection, are you sure Scintilla has a default binding for `ctrl+click` that does multiple selection? If not you need to add it, or add it to Geany in place of the code you deleted.
Per comments above I expected some parts not to play nicely with multiple selections
I would expect _everything_ to simply ignore multiple selections, and just read the main selection and operate on that. And thats where the "significant change" part above comes in.
The `enable-multiselection` branch is not in the Geany repository, or any PR (AFAICT) so it a private one at best in that persons github repository.
PS removed the backticks around your link so it would work, markup is ignored inside backticks.