I'm a bit confused - agent vs. agentless isn't obviously correlated to continuous vs. on human action to me. Write a cronjob / systemd timer / scheduled task / Jenkins job / Travis cronjob / GitHub Actions scheduled event / CloudWatch + Lambda / whatever you like to run your Ansible playbook, from one machine/container/whatever, on your entire fleet. (It's certainly no harder than writing a cronjob or whatever to run your config management on every machine - if you can schedule tasks on all your machines, you can certainly schedule them on one.)

That gets you the standard advantages of agentless setups, including not requiring the runtime of your config management tool to be everywhere, being able to reprovision ephemeral + immutable cloud resources, and being able to centrally report errors, without any more risk of configuration drift or bitrot.