The nginx image uses the nginx user.

_deployment/Dockerfile.nginx

 FROM nginx:mainline-alpine
-COPY --chown=http:http ./_deployment/nginx.conf /etc/nginx/conf.d/default.conf
-COPY --chown=http:http ./frontend /srv/http
+COPY --chown=nginx:nginx ./_deployment/nginx.conf /etc/nginx/conf.d/default.conf
+COPY --chown=nginx:nginx ./frontend /srv/http