You need to access the WordPress files on your hosting account and remove the plugin’s folder.
Reading your other post here, it seems you’re not entirely sure who your host is. I’m not convinced it’s WordPress.com.
If you can share your domain name, I could run some checks and send you in the right direction.
Hello there! I found the bugging Plugin: It was not Sucuri, but “Alfred the Assistant” from IONOS. I deactivated it via Duckzilla. Now I can access Plugins + Dashboard. Thanks for your reply! Much appreciated