according to bobby at brewhardware the solar mppt version of this pump can still be somewhat controlled with pwm controllers...
The new version is actually made for brewing applications and comes with an actaul dual input pwm board designed to be used with it.
https://store.brewpi.com/mashing/brewing-pumps/td5-24v-brewing-pump
They are a bit pricey but not really because the tax comes off at checkout and I got it in like 3 days from Europe.
it is possible you can open the pump up you have and remove the mppt chip thats fighting the pwm. I am unsure but as mentioned above I want to say the older style mppt pumps use actual 17v motors and the mppt adjusts it for peak performance (thats the way the original Ts5 plastic version pumps worked) It looks like the newer style td5 uses an actual 24v motor.
the whole idea of the mmpt was whether the solar panel was in full sun of partial shade the voltage could go from say 22v down to 12 v and the pump speed would stay relatively the same. (using 24v solar panels)