Install tinyMCE

We could download the last version using npm i tinymce@^7 and copy it into /var/lib/trytond/www
We need to set the license to GPL: https://www.tiny.cloud/docs/tinymce/latest/license-key/#use-tinymce-with-the-gplv2-license.
We may download also the languages from https://download.tiny.cloud/tinymce/community/languagepacks/7/langs.zip