I'm not sure it is a dark pattern, but at first glance (to me) it reads a bit like the "Allow all" and "Reject all" buttons just toggle the options, and then one needs to press "Confirm my choices", particularly on mobile with how the stack.

The confusion would probably be quickly resolved when the dialog closed after clicking Reject all, but perhaps changing the wording of "Confirm my choices" to something like "Allow checked" would make it more clear it is a sibling of the other two buttons (and that checked means allowed).

No, this is confusing. Please iterate on this. Two buttons shouldn't do the same thing depending on state.

I get it: the intent is that there's always a quick, one-click way to broadly consent/not consent. But with how this is designed, after clicking Accept All or Reject All, I'm left wondering what Confirm My Choices did. (Maybe it persists my consent on subsequent visits? I dunno.)

Perhaps, "Confirm My Choices" (or better put, simply "Submit") stays, but change the "Accept All" and "Reject All" buttons to "Select All" and "Deselect All" buttons, respectively. These buttons should only serve to change the state of the checkboxes without submitting.

If there were some checkbox still checked (perhaps in some submenu that needs to be expanded), then "confirm my choices" might obviously have a different consequence. That might not apply here, but I am pretty sure I have seen that on other sites before. I am not a laywer, but "confirm my choices" just sounds like it could be interpreted in a way benefitting the website owner's interests in some cases even if everything is unticked, whereas "Reject all" is a very clear statement of disagreement. Similarly, you wouldn't say "I agree to everything on this list after I have removed all items", but "I disagree with anything on that list you gave me". But that's a general pattern it seems.