Hi Tomasz,
Thanks for contacting Syncfusion.
Context menu support is available only from 17.2.28-beta version. Please delete @syncfusion packages from node modules and package-lock.json from your project. And run the command ‘npm install @syncfusion/ej2-vue-gantt@17.2.28-beta’ to install new packages.
Please get back to us if you require further assistance on this.
Regards,
Jesus Arockia Sankaran S