After updating plugins theme seems to be locked ?? "The theme 'kenshin-kenshinschool' is locked and cannot be used. Please duplicate this theme or create a child theme. October\Rain\Exception\ApplicationException" All .env and cms.php values are right, even after change values no change of this error exception. I am stuck... Help appreciated

This is a new feature of October CMS 2.0 since the theme is installed with composer, there is potential for data loss. If you customise the theme, composer may delete your customisations when the theme updates, so the theme is locked for protection.

https://octobercms.com/docs/cms/themes#child-themes

You can simply copy the entire theme to a new directory and delete the .themelock file (duplicate the theme) and then it is safe from composer overwriting it.

Hope this helps!