you still didn’t add any logs and referring to a 5y old tutorial doesn’t tell us if you follow the guide exactly or made some changes (which I assume you did, especially from the the Nextcloud collabora docker loading document fails I have the feeling you are doing strange things with local IPs or maybe no TLS which is always bad). Please add logs from all components, especially browser F12 logs might be interesting as copy&paste is a client-side task.