What many have not thought of is that the uploads.ini requires the correct authorization.

Especially with dockremap user e.G.

chown -R 100000:100000 uploads.ini

Otherwise, this is exactly what happens in the container:

root@c5cf31571ea5:/var/www/html# cat /usr/local/etc/php/conf.d/uploads.ini
cat: /usr/local/etc/php/conf.d/uploads.ini: **Permission denied**