Based on Planck's constant, is there an 'ultimate' frequency, too?

Dimension of 'frequency' is T‾¹.

Since Planck time is about 10‾⁴³ second, the 'ultimate' frequency could be about 10⁴² Hertz. A bit of Fourier analysis (Fourier Transform) could help in that.

I believe you are asking if there is a Planck wavelength which of course would an ultimate frequency. Presumably that would be a wavelength of two Planck Lengths per two Planck time, otherwise there would not be a distinct waveform, and I suspect there is such a maximum energy content for a photon. Chances are it would decay into a matter anti-matter pair long before reaching that level.

? you mean frequency limit?

? Based on Planck's Constant?

There is no limit to possible frequencies CAUSED by the value of Planck's constant... Does that answer what you were attempting (and failing) to articulate in a question?

Some theories of quantum gravity have as an indivisible unit the Planck time, it should be obvious that this limits the frequency of anything which agrees with those theories. However more complex waves can be "decomposed" harmonically which would allow the assignment of sub-planck time frequencies as (abstract) components of hypothetically real wave forms.

Be more specific. What do you mean ultimate frequency? Do you mean infinite?