When using org-capture with :clock-in or when starting the clock manually when writing the note, then after canceling the note using C-c C-k, the clock continues as can be seen in the modeline.
Reproduced also in a clean 'emacs -Q' setup. Emacs : GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin19.6.0, NS appkit-1894.60 Version 10.15.7 (Build 19H15)) of 2020-12-01 Package: Org mode version 9.4 (9.4-53-gc97446-elpaplus @ /Users/df/.emacs.d/elpa/org-plus-contrib-20201130/) Daniel Fleischer