The following options are set and I can download collections via UI without a login.

GALAXY_ENABLE_UNAUTHENTICATED_COLLECTION_ACCESS = True
GALAXY_ENABLE_UNAUTHENTICATED_COLLECTION_DOWNLOAD = True

However, when attempting to install via ansible-galaxy, I get this message:

ansible-galaxy collection install -s https://my-galaxy-sandbox.com/api/galaxy/content/published/ lmt.ac_galaxy_demo -vvv
ansible-galaxy 2.10.17
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/xxx/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/xxx/.local/lib/python3.8/site-packages/ansible
  executable location = /home/xxx/.local/bin/ansible-galaxy
  python version = 3.8.10 (default, Nov 26 2021, 20:14:08) [GCC 9.3.0]
Using /etc/ansible/ansible.cfg as config file
Starting galaxy collection install process
Process install dependency map
Opened /home/xxx/.ansible/galaxy_token
Processing requirement collection 'lmt.ac_galaxy_demo'
ERROR! Error when finding available api versions from cmd_arg (https://my-galaxy-sandbox.com/api/galaxy/content/published/) (HTTP Code: 403, Message: Forbidden)

I am able to install if I provide a token, but I think I should be able to install without login as I can download in UI.

ansible-galaxy collection install -s https://my-galaxy-sandbox.com/api/galaxy/content/published/ --token 7277e4b4cdd31f7fcff3399daea3aec06ab378d9 lmt.ac_galaxy_demo -vvv
ansible-galaxy 2.10.17
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/xxx/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/xxx/.local/lib/python3.8/site-packages/ansible
  executable location = /home/xxx/.local/bin/ansible-galaxy
  python version = 3.8.10 (default, Nov 26 2021, 20:14:08) [GCC 9.3.0]
Using /etc/ansible/ansible.cfg as config file
Starting galaxy collection install process
Process install dependency map
Opened /home/xxx/.ansible/galaxy_token
Processing requirement collection 'lmt.ac_galaxy_demo'
Collection 'lmt.ac_galaxy_demo' obtained from server cmd_arg https://my-galaxy-sandbox.com/api/galaxy/content/published/
Starting collection install process
Installing 'lmt.ac_galaxy_demo:1.0.0' to '/home/xxx/.ansible/collections/ansible_collections/lmt/ac_galaxy_demo'
Downloading https://my-galaxy-sandbox.com/api/galaxy/v3/artifacts/collections/published/lmt-ac_galaxy_demo-1.0.0.tar.gz to /home/xxx/.ansible/tmp/ansible-local-325184907a_n21/tmp8zh0f7rv
lmt.ac_galaxy_demo (1.0.0) was installed successfully

Installed versions:

pulpcore==3.15.1
galaxy-ng==4.4.1
pulp-ansible==0.10.1
pulp-container==2.8.3