I would suggest adding "UID" and "GID" environment variables to the container, and set them to the numeric values for user and group numbers that show in place of your name when you use "ls -an" inside of the "mount" folder (they will probably be the same number).
For example, if inside your mount folder you see:
ls -an
total 12
drwx------ 2 1001 1001 4096 Mar 27 13:54 .
drwxr-xr-x 3 1000 1000 4096 Mar 27 13:51 ..
-rwx------ 1 1001 1001 0 Mar 27 13:54 hello.txt
-rwx------ 1 1001 1001 4 Mar 27 13:54 test.txt
Then set UID: 1001 and GID: 1001
I get the same error as you when I copy your docker-compose and try to access a folder owned by my user. When I add the UID and GID of my user id to the docker-compose (1001 for me), the error goes away.