Byobu moved to the fof namespace and tagged a new version which fixes the installation and adds support for mariadb. Install using:
composer require fof/byobu
This should remove flagrow/byobu, if it doesn't please do so by running
composer remove flagrow/byobu
Then re-enable the extension in admin, or run
php flarum migrate
php flarum cache:clear
If you run into any issues, please let me know.