Went through the help system in detail but no mention of new "linear or hold" options for keyframes.
Finally noticed that the URL launched by F1 help system was still
https://help.cyberlink.com/stat/help/powerdirector/20/win/enu/14_00_00_mask_designer.html
replace the 20 with 21 and now I have the updated info!
https://help.cyberlink.com/stat/help/powerdirector/21/win/enu/14_00_00_mask_designer.html
Hope this helps someone save some time! Cheers, Scott