Docker volume mount and permissions: www-data on host (33) becomes xfs (33) in Alpine Linux – Nginx

I have trouble with a Directory mount from my host in a docker container:

• Alpine Linux includes user xfs (33) and group xfs (33), with no www-data
• the files on host are owned by www-data (33)
• I need these files to be accessible by nginx inside the nginx:alpine docker image

This is a fullstack situation: I am using a service stack to make files available on local lan.
the stack uses nginx:alpine, images are made available – so I cannot easily modify the Dockerimage.

Is there anything that I can do that xfs inside the Alpine Linux image does’t get user and group id 33?

I tried to set PUID and PGID in the docker-compose.yml,
but it doesn’t work (I also have trouble understanding this):

services:
celeryworker:
    environment:
      - PUID=33
      - PGID=33

Minimal reproducable example:

Files on the host:

cd /mnt/nfs/folder1
ls -alh
>-rwxr-xr-x 1 www-data www-data 3.5M Sep 21 15:41 '02 - track.mp3'
ls -alhn
>-rwxr-xr-x 1 33 33 3.5M Sep 21 15:41 '02 - track.mp3'
less /etc/passwd | grep www-data
>www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin

docker-compose.yml

version: "3"

services:
  celeryworker:
    restart: unless-stopped
    image: funkwhale/funkwhale:1.0.1
    networks:
      - default
    depends_on:
      - postgres
      - redis
    command: celery -A funkwhale_api.taskapp worker -l INFO --concurrency=0
    environment:
      - C_FORCE_ROOT=true
    volumes:
      - "/mnt/nfs/:/music:ro"

Files in the container:

docker exec -it funkwhale_celeryworker_1 /bin/bash
cd /music/folder1/
ls -alh
>-rwxr-xr-x    1 xfs      xfs         3.4M Sep 21 13:41 '02 - track1.mp3'
ls -alhn
>-rwxr-xr-x    1 33      33         3.4M Sep 21 13:41 '02 - track1.mp3'
su xfs
>This account is not available
less /etc/passwd | grep xfs
>xfs:x:33:33:X Font Server:/etc/X11/fs:/sbin/nologin