I'm having a similar issue. The UI is laggy - the whole thing (including Now time and meters) momentarily freezes every few seconds which makes adjusting dials and EQ really tricky. It still happens even when all effects are off and engine load is about 10% (audio load 4%).
The attached photo shows the NowTime stuttering. It doesn't look like much but each time it freezes the whole UI freezes, so it interupts mouse clicks, drags etc.
I upgraded from Windows 10 1909 to 20H2 this week, the same time as updating to the April Cakewalk build. It was working fine on the old windows build with previous cakewalk version.
Specification: Cakewalk 2021.04 (build 144), Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz 2.59 GHz, 16 GB RAM, Windows 10 Pro (20H2). All latest drivers.
PXL_20210505_131907407 (1).mp4