This is a generic error. Check your nextcloud.log as described in the support template.
I had to restart the docker compose set up, I saw that the Nextcloud container was recreated/updated.
I see you’re using the latest tag. You may want to use a more specific tag to avoid surprising major version bumps. See LSIO’s image docs.
Webtools says it cant load favicon
Failing favicon retrieval won’t prevent anything from functioning (to this degree). This is likely a red herring.