Use nextcloud instead of sftp on my VPS?

Nextcloud version: 15
Operating system and version: Ubuntu 18.04
Apache or nginx version: apache2
PHP version : 7.2.13

I’m running nextcloud on docker
I’d like to use nextcloud instead of a sftp in order for users to upload files to a given folder, shared with another container.
I did specify the following line in docker-compose for nextcloud:
- ${PWD}/docker/nextcloud:/var/www/html
- ${PWD}/docker/lizmap/project:/data:rw
whereas the second line is the folder I need to upload files to.
When I open nextcloud GUI I can’t see or mount the given folder.
Can this be done? how?
thank for pointing me in the right direction