> FrankenPHP sounds promising, but in reality it is a weirdo: no one uses PHP without modules.

You usually build the modules yourself in the Dockerfile, for example for the "pgsql" module:

    RUN apt-get update && apt-get install -y libpq-dev && docker-php-ext-install pdo_pgsql && apt-get remove -y libpq-dev && rm -rf /var/lib/apt/lists/*

    http://:80 {
        # rest of the Caddyfile directives
    }