Either youtube backed off a change, or embedpress plugin installed a change.
In any case this AM, April 16, 2021, embedded youtube playlists are now playing correctly in wordpress as in the past. Issue resolved for the time being.
This has been resolved by Mr. Arno Welzel.
There is a bug in the Essential Blocks plugin v2.2.0 by WPDeveloper.
There is CSS rule in that plugin which turns off all checkboxes globally.
This has been reported to WPDeveloper. The temporary fix is to deactivate Essential Blocks pending code fix by WPDeveloper.
