I managed to set it up this way:
in compose file mount location of user home dir
NEXTCLOUD_MOUNT=/srv/dev-xxxxx/your_home_dir_from_omv/
your_home_dir_from_omv is dir you set on OMV>users>settings
In NextCloud need to enable external storage and after that in Administration settings >External storage add location of your user dir
Folder name: for example MyOMVHome, name that will appear in NextCloud
external storage: local
Configuration: location of your username dir, like
/srv/dev-xxxxx/your_home_dir_from_omv/username
available for: pick nextcloud user
your user home dir is owner by username and nextcloud user www-data will not have permissions.
First i tried with ACL, but with that new files created with NextCloud are owned by www-data and your username will not be able to change that file
So i created new user group, for example group_name used in the code below , add my username and www-data to that group and change owner of my username dir
You can create group using OMV web and add your username into that group. But you need to add www-data with:
sudo usermod -a -G group_name www-data
after that fix permissions
sudo chown -R username:group_name /srv/dev-diskxxx/your_home_dir_from_omv/username/
All new files need to inherit the parent dir group ownership
sudo chmod g+s /srv/dev-diskxxx/your_home_dir_from_omv/username/
The group must have write permissions
sudo chmod -R 775 /srv/dev-diskxxxx/your_home_dir_from_omv/username/
After that you can force nextcloud to scan files in external storage with
docker exec --user www-data nextcloud-aio-nextcloud php occ files:scan --all
Hope I did not forget something 