[elago]

I wouldn't say that's the problem. You do not need to register a new account to see an instance's timeline.

For example this page shows the instance's timeline without logging in: https://mastodon.sdf.org/about

If you like someone's toots there, you can follow and message any user on SDF's instance from your account on any other instance.

As mentioned elsewhere, the only thing you would gain by creating an account on sdf.org is to have your toots appear by default in the local timeline of other sdf.org users.