I've tried it at a lot of hours around the clock, so I doubt that I should've missed it for that many attempts (at some point the offset should be mute).

Again, the cb:date substitution since it was created has always applied the offset. I don't know what more to say regarding this. Maybe at some point you had UTC timezone set in your account or for the site so it wasn't noticeable.

And how do I get the 'users' trigger to show the debug info? I've enabled debugging for the site, but I still don't see it.

Enable debug mode in Joomla global configuration and enable debug under the Parameters tab of your auto action. If there's any debug information to output it'll output to Joomlas message queue and should show as an error at the top of the page. It only outputs debug information in event of access failing, condition failing, or error in the action. Not all triggers have output so some may not be able to output debug information. You could also be using the wrong trigger and expecting it to work when it won't.

I would love to test out if the offset has any difference to it, but as I can't get the debug shown for the users trigger currently it's impossible, and of course the 'big dates' are closing in (30/9+1/10) for my auto actions.

Just use [cb:date format="m-d" offset="UTC"/] and you'll be fine as it'll always compare to UTC. The cb:parse function="date" usage is always UTC by default.

I could see debug in 6.x but in the New version it doesn't show any debug.

I've no idea what your action configuration is so I've no idea what to tell you. CB Auto Actions 7.0.0 is a rewrite. It was rewritten from the ground up. It's using namespaced classes and proper error setter/getter. The errors are output to Joomlas message queue. If the message queue gets purged you won't see them. So depending on when you're doing this the message queue may get emptied (only seen this happen during logout operations). Aside from that you must ensure debug mode in Joomla is enabled and that you've debug enabled in your auto action.

And I still dont understand how utc can change the date comparison by a Day.

It's not. You weren't using UTC when getting the current date. You were offsetting by whatever the server offset was set to or by whatever the viewing users offset was set to as again cb:date substitution is always offset unless you specifically set it not to with offset="UTC".