I had the same issue with Poser 11 slowdown as you did following the forced Windows update. I am running Poser 11.3.818.

After checking the updates in settings, I found that there were optional updates that Windows did not inform me of until I looked. These are the ones listed in the attached image as having been applied 3/27/2021. After applying the optional update and restart, I found that Poser responded much better than it did. I'm not sure it's quite as fast as before, but much faster than after the first update. Usable now with no "click lag" on graphic UI items, which had been my main problem, also preview movement much improved.