Operation Not Permitted

I'm on Ubuntu 22.10, with docker-compose 1.29.2 and Docker 20.10.21, both installed using apt (not snap), on a DigitalOcean server.
I followed the installation instructions at https://docs.mattermost.com/install/install-docker.html exactly.

• For step 4, I copied a fullchain.pem and privkey.pem I already had for the same domain to the specified directory with tthe respective names.
• I skipped the optional step 5.
• For step 6, I deployed using the included NGINX.
  After running sudo docker-compose -f docker-compose.yml -f docker-compose.nginx.yml up (not detached to see the output), I get:

Creating network "mattermost" with the default driver
Creating docker_postgres_1 ... done
Creating docker_mattermost_1 ... done
Creating nginx_mattermost    ... done
Attaching to docker_postgres_1, docker_mattermost_1, nginx_mattermost
mattermost_1  | exec /entrypoint.sh: operation not permitted
postgres_1    | exec /usr/local/bin/docker-entrypoint.sh: operation not permitted
nginx_mattermost | exec /docker-entrypoint.sh: operation not permitted
docker_mattermost_1 exited with code 1
docker_postgres_1 exited with code 1

I restarted the server without any other containers running (ports were free), I tried step 6 without the included NGINX, I ran sudo chmod 777 -R ., I ran everything as root, I searched the web, nothing worked. Is this a bug? Did I do everything correctly? What can I do to make this work?

Start with docker-compose.yml and docker-compose.nginx.yml, then inspect the reported container entrypoints: /entrypoint.sh, /usr/local/bin/docker-entrypoint.sh, and /docker-entrypoint.sh. Reproduce the command in the issue and compare the host, Docker, image, mount, and permission details. Done means identifying the cause of the operation-not-permitted errors and documenting a verified working deployment or a confirmed product bug.