OK I found a new way to directly run the macro using bixby key but it's a little bit tricky. Go to Bixby key setting - choose double press to open Bixby - disable "use single press" option.
Next the tricky part is to identify the logcat message when you single press the bixby key. I use the app...
Just in case you still need a possible solution, I hope this way will work for you.
Go to Bixby key setting - choose double press to open Bixby - then set use single press to open an app (should be a small app and you never use it) - next go to Macrodroid and create a new macro.
Trigger
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