Only one human per machine. If you need to share the machine, make multiple containers and give everyone a separate container.

You don't run any services where more than one person shares responsibility for managing that service? E.g. kubernetes. That is just one guy holding it up?

In an on-prem cluster, yes one guy or a few sysadmins who either share passwords or can somehow put their keys in the authorized keys file and ssh.

In the cloud, AWS/GCP let or not let an IAM user reach a server.

That's convenient but doesn't scale and really not too great for security for a bunch of reasons, but it can work great for smaller teams and minimize friction.

Signed ssh certs make your life easy here

Maintaining your own PKI isn't exactly easy unless it's your full time job.

Its fairly easy to get setup and after done correctly pretty low maintenance. But i have done it a few times at this point.