This is Emacs 29.4. I haven't yet tried it on an Emacs 30 build and latest ELPA modus-themes-20241028.849.
Starting with vivendi from a clean restart.
M-x modus-themes-toggle to operandi.
Now M-x make-frame with operandi in effect. The new frame is screwed up.
I've added this stanza to solve the issue.
;; these parameters are not correctly copied by make-frame.
(add-to-list 'frame-inherited-parameters 'background-mode)
(add-to-list 'frame-inherited-parameters 'background-color)
(add-to-list 'frame-inherited-parameters 'foreground-color)
Now after the toggle, the new frame looks fine:
FYI, clone-frame works fine but not make-frame.