I would probably use their docker run command (image name doesnt contain x86) from github, which can be converted to docker-compose with sites like:

https://www.composerize.com/

And it becomes something like this:

name: <your project name>
services:
    nextcloudpi:
        ports:
            - 4443:4443
            - 443:443
            - 80:80
        volumes:
            - ncdata:/data
        container_name: nextcloudpi
        image: ownyourbits/nextcloudpi
        command: $DOMAIN
volumes:
    ncdata:
        external:
            name: ncdata

But again, im not expert and I was running linuxserver.io image on my pi (I still run it, but upgraded server to x86 PC)