I'm still having this problem, for two days now. It's not killer, but it's annoying.
I've restarted Chrome, KBM, and my computer several times and it's made no difference. I've been considering reinstalling Chrome, but that's a huge amount of work to reinstall all extensions, etc. Not worth it for the annoyance level.
Meanwhile, I'm going to try replacing the New Google Chrome Window action with a piece of AppleScript to do the same thing and see if that keeps me going for now.
Fortunately, I had a copy of an old version of Google Chrome.app around, from version 90-0-4430. I have that because the next version of Chrome changed something and broke the ability to do cut-n-paste of tab trees in Tabs Outliner. So I let Chrome do its auto-update thing and when I need to do a cut-n-paste in Tabs Outliner, I shut down Chrome, start up the older version, do my TO reorganization, close Chrome, and then restart whatever the latest version is.
So I tried running that older version of Chrome. And when I did, I got this permissions dialog:
I said OK and then tried the problematic KBM action. It worked fine. So I closed that older Chrome and opened it again at the current version. I got that same permissions dialog again. I said OK again, and now my KBM macros, using that New Google Chrome Window action, work as expected.
After finding the above solution, I discovered there was another clue available to me, in the KM log file, ~/Library/Logs/Keyboard\ Maestro/Engine.log. There were multiple entries like this:
2022-02-08 18:50:11 Async NSAppleScript error 2022-02-08 18:50:11.117 CompileAppleScript[8548:198675] Keyboard Maestro Internal AppleScript Execute Error: Not authorized to send Apple events to Google Chrome.
So that tells me that, as I was asking above, KM uses AppleScript to tell Chrome to open a new window. I'm not sure that it would have told me how to fix it, but it would have reassured me that I was on the right track. My next step would have been to Google "Not authorized to send Apple events to Google Chrome."
I would LOVE to have a way to look at that log file directly from the KM editor.