I got the URL from the 3 dots in the same pane as the title of the note for “more options” and then selecting “copy Obsidian URL”
If I paste it in the web browser manually as you suggest and click enter, the browser asks if I want to open the page in Obsidian, which seems to work when I click enter - but when I put Open URL as an option in Keyboard Maestro I get an error message and when I put open a new tab in Safari with the URL pasted, it doesn’t open the URL unless I click enter manually.
The fact that web browsers have no trouble opening the URL seems to prove there’s nothing wrong with it. It must be something with the KM action, but I can’t help with that because I don’t use it. Sorry.
Maybe try looking at the KM docs and see if there’s some setting you’ve missed.
Given the many type of Keyboard Maestro variables, it’s hard to say the exact sequence/pattern of % characters in the URI that will or won’t cause the error. As a result, sometimes an Obsidian URI will work with the Keyboard Maestro Open URL macro out-of-the-box (IOW: copy/paste) and sometimes you’ll see the orange error.
A simple way to continue using Open URL macro (or any other that will accept and process a URI), is by setting the Process setting (in the gear menu) to Process Nothing:
Thanks to @gglick, at the Keyboard Maestro Forum, for this.
FYI: The downside is, you will no longer be able to pass Keyboard Maestro variables into the url field of this specific action. Which limits more advanced Keyboard Maestro/Obsidian interaction.
Using the Execute Shell Script macro, mentioned above by @phy, should work. And you’ll pass in the Keyboard Maestro variable like this: $KMVAR_variable_name_here