Best not to use bind mounts with volumes.  Better to use bindfs outside of docker to mount them elsewhere with an owner map.  Install if need be

on host make a nextcloud user with id 82 (which is www-data in fpm-alpine container)

must run bindfs as sudo for mapping

sudo bindfs --map=nextcloud/sysadmin /var/lib/docker/volumes/nextcloud_user-files/_data /data/nextcloud/user-files
sudo bindfs --map=nextcloud/sysadmin /var/lib/docker/volumes/nextcloud_src/_data /data/nextcloud/src
<!-- sudo bindfs --map=nextcloud/sysadmin /var/lib/docker/volumes/nextcloud_user-files/_data /data/nextcloud/user-files -->

sudo mv 
sudo bindfs -o nonempty --map=sysadmin/nextcloud /data/nextcloud/user-files /var/lib/docker/volumes/nextcloud_user-files/_data 

sudo bindfs -u nextcloud -g nextcloud  /data/nextcloud/user-files /var/lib/docker/volumes/nextcloud_user-files/_data 
bindfs -u nextcloud -g nextcloud  /data/nextcloud/src /var/lib/docker/volumes/nextcloud_user-src/_data 

# adding container directory
apk add bindfs --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing
addgroup --gid 1000 host && \
adduser -u 1000 -G host -g "" -D -H host && \
mkdir -p /source && \
mkdir -p /user-files &&\
bindfs --force-user=host --force-group=host --create-for-user=www-data --create-for-group=www-data --chown-ignore --chgrp-ignore /var/www/html /source &&\
bindfs --force-user=host --force-group=host --create-for-user=www-data --create-for-group=www-data --chown-ignore --chgrp-ignore /var/www/data /user-files