I found a way out of the Plugin Update Loop of Hell. Posting here - it might help others who get no better suggestions ...or any suggests at all from the forum.
Credit to https://poodll.com/escaping-plugin-dependency-hell/
That page provided a link http://YOUR-MOODLE-URL/admin/tool/installaddon which gets you off the update page.
From here I could navigate to Admin / Plugin
Find the offending plugin - hope it's not crucial - uninstall it.
Updates of other Plugin Check Update Loop of Hell should now be ok - update remaining plugins
Wonder how you are supposed to get the uninstalled plugin back.
Realise you now have to do a full site update
Shudder.