Initially I did not use any DDF, as the blind itself does work and can be controlled with the deCONZ Desktop App - but not with the PWA Web App.
I looked into the following two DDFs (this one from the referenced thread, mentioned above and that one from MR #6110). None of the two solve the problem, I have here: The PWA / Web App still adds the transitiontime parameter, whether I use one of the two DDF or leave them out.
But this helped me to do some testing: When I remove both states (state/bri and state/on), being deprecated in MR #6110, then the Rest API complains about all three parameters, missing. So this does not motivate PWA to use the state/lift property.
Should/Will PWA consider state/lift some time in the future? This parameter is exposed in the DDF of MR #6110 (and the DDF for KADRILJ)
It might be possible, to add a state/transitiontime parameter. But that parameter will never have any functionality, so defining (and publishing?) it seems more than wrong.