I had a case where my WP was working but /portal had Critical Error in this case I wanted start from the beginning. Uninstalling plugin from WP Admin console didn`t help so I had to remove all DB tables: wp_fcom tables:

DROP TABLE `wp_fcom_chat_messages`, `wp_fcom_chat_threads`, `wp_fcom_chat_thread_users`, `wp_fcom_media_archive`, `wp_fcom_meta`, `wp_fcom_notifications`, `wp_fcom_notification_users`, `wp_fcom_posts`, `wp_fcom_post_comments`, `wp_fcom_post_reactions`, `wp_fcom_spaces`, `wp_fcom_space_user`, `wp_fcom_terms`, `wp_fcom_term_feed`, `wp_fcom_user_activities`, `wp_fcom_xprofile`; 

Once it was done I was able to install the plugin again.
If a new beta plugin was released in a meantime then I am not sure if I can replicate this issue.