To review we have installed an Odoo 16.0 live demo: https://odoo-gantt.bryntum.com/web/login
Login: demo/demo
We will push bug fixes and enhancements to the Odoo repository regularly. To get those fixes you can download the latest module version in a zip file from Odoo's app store page. In the module description is a list of latest changes.
https://apps.odoo.com/apps/modules/browse?search=bryntum
You have to log in with the account that is used for the purchase of the module.
After download, add (unzip) the upgraded gantt module to the addon-path. Or, depending on your Odoo installation, merge the code in the zip file to your repository.
Then follow the steps provided in Odoo's upgrade manual
https://www.odoo.com/documentation/14.0/applications/general/apps_modules.html
In some cases (fresh install) a restart of the Odoo server is required to include the module sources in memory of the Odoo instance. See the links below for corresponding command line options.
https://www.odoo.com/forum/help-1/upgrade-module-by-command-line-157627
https://www.odoo.com/forum/help-1/how-to-force-odoo-to-upgrade-modules-immediately-after-start-161333