Loading documents in a mobile browser fails

thank you for update. default support template might be no very good for CODE issues. Please describe your config im more details - CODE built-in or separated, which technology etc…

Take a look at this guide: Nextcloud Collabora integration

You might need to focus on the client side where “F12” tools are useful - this is not easy on mobile but there are ways as well. Start checking you can visit all the URLs from your mobile. problems specific to mobile often result from the fact such devices heavily prefer IPv6 over IPv4.