The playbook can install and configure synapse-auto-invite-accept for you.
See that project’s documentation to learn what it does and why it might be useful to you. In short, it automatically accepts room invites. You can specify that only 1:1 room invites are auto-accepted. Defaults to false if not specified.
If you decide that you’d like to let this playbook install it for you, you need a configuration like this:
matrix_synapse_ext_synapse_auto_accept_invite_enabled: true
matrix_synapse_ext_synapse_auto_accept_invite_accept_invites_only_direct_messages: true