Is Document Server integration(in the apps section) working?

I’m running NC on unraid. It runs quite well, but I’m having problems with Only Office. I was watching a Space Invader One video from Feb 2020 where he was saying that the native document server plugin(from apps) is not working but he expected it to be working soon. Been 3 years now and it still appears it isn’t working. Is that known to be working, such that I should double check my configs? I’m getting the error whilst trying to edit a file ‘ONLYOFFICE cannot be reached. Please contact admin.’

Great help everyone. Want to thank you.