If we clear cache after any update in admin panel it gets an exception error that "Unable to register extension "nochso\HtmlCompressTwig\Extension" as extensions have already been initialized ". How it is solved? Screenshot attached - https://ibb.co/SJYRhHQ

Hello!
Do you have installed a Octobercms Minification/Compress Plugin? I guess HTML minify plugin. So the problem has to do with the plugin and not with theme.