Can't add Quicksilver keyboard shortcut trigger I'm setting up a new mac and I can't seem to set the keyboard shortcut to triggers I'm creating, as I've always been able to do before.

I'm able to create the trigger, but then when trying to edit it, after clicking the (i) and attempting to click either the (empty) shortcut box, or the "edit" button next to it, the box flashes "Set Keys" for an instant, but then it disappears and I'm not able to set the shortcut.

See here (you might not be able to see the flash of "Set Keys" because of the gif encoding, but it's there albeit very brief:
This is a known issue.

https://github.com/quicksilver/Quicksilver/issues/2361

It has been fixed and a new version will be released this week sometime.

Until then, you can download an older version to customize the keyboard shortcuts. Once they’re set, you can go back to the latest version, or wait for the next update.