Solved on my local development environment (but not on odoo.sh):

6 js files located in the knowledge addons should be corrected accordingly by adding the required static id = 'xxxx', so that the error described above can disappear:

export class EmbeddedClipboardPlugin extends Plugin {
    static name = "embeddedClipboard";
    //added by me:
    static id = "embeddedClipboardPlugin";