The Set Position in Viewport node does affect UserWidgets position. It keeps it
4.19.2 (CL - 4033788), 4.20.3 (CL - 4369336), 4.21 (CL - 4465720), 4.22 (CL - 44654877)
Expected: User widget reflects the change in viewport position
Result: User widget keeps the same position
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-65214 in the post.