@pwwuk This is fine, i get the picture now
I did connect to your instance nice videos of paris trip btw 
What i understood :
You use codium with a ssh plugin to operate a Oracle Cloud Ubuntu. This is a small difference from the vultr used in the tutorial.
The other change is install directory on /home/ubuntu/docker/peertube instead on /opt/peertube in the tutorial and log as ubuntu instead of root.
docker install of peertube what done using standard docker peertube installation.
Within your docker-volume you will find all persistent data, if you remove it you will mainly lose your videos and related informations, well everything about peertube 
What is difficult with docker is that what you see on your host will be named, organized differently within docker and even can be temporary there only accessible within containers. All that is visible in docker-compose, mainly mappings of volumes.
I will come back with more hints, one thing about this docker install is that webserver provided is somehow a convenience to make things faster. in many case a web server is already existing and configuration is done in it, webserver part of docker-compose is then commented out.
In my personal case i don’t use docker, my peertube install is fully done manually under a debian host and i manage my nginx in my way.
Quickly to get things better is to stop docker-compose, from within docket/ubuntu directory edit peertube from docker-volume/nginx , ( or even remove it ? normaly it should be regenerated with standard defaults ) and restart docker-compose.
Usual way to deal with docker is to not change thing within them but change their configuration and restart them. And in our case just to use new nginx configuration it is mandatory to restart cotainer, that can somehow tweak configuration again.
By default with correct .env setting this should work, so there can be problems with the host configuration itself. From here i would ask : what sizing of memory did your pick for your host in Oracle Cloud ?
i will come back later with more hints.