I have been using NotePlus for two years approximately.
Recently, after upgrading to iPadOS14 (I’m using iPad pro) I have noticed the writing experience became laggy.
It had lost the “real pen on paper” feeling I liked so much, and the lines drawn are now a few milliseconds behind. Scrolling the notebook is also not smooth.
My son use NotesPlus too with iPad 10.2 but with iPad OS 13, and it works fine.
Up until recently, iOS14 was in its beta stages, but it has now been release to the public.
I gave the support team a head-up on this, but it seems they haven’t done any testing, and sadly my guess is many other users will experience the same issues after upgrading to iOS14.