Just clone this repo into your apps directory (Nextcloud server installation needed). Additionally, npm and Node.js are needed for installing JavaScript dependencies and building the frontend code.
Once npm and Node.js are installed, this can be done by running:
npm ci
npm run dev
You will need an working on-premise Office Online server which has added the Nextcloud server as a trusted host for WOPI. The cloud-based Office 365 is not supported.
Enterprise users who need a more reliable and scalable solution can take advantage of Nextcloud GmbH's optional support contract for Office Online integration. Find out more about Enterprise support over here: https://nextcloud.com/enterprise/