Unlocked account with "Unlisted" post setting seems to be the closest to a normal public Twitter account (with the exception that you won't show up in searches here if you're set to unlisted)
Locked account with "Followers-only" post setting is the closest to a locked Twitter account
Follow
Interestingly, you can post Followers-only posts on a public account (which means they're viewable only by followers, but anyone can follow you to see them)
You can also post Public/Unlisted posts on a locked account. which means you can separate between public-facing posts and private posts on the same account
To be honest I find these settings very interesting and handy to me, but I can absolutely see them being confusing or opaque
I *do* find it to be just a little bit annoying to make sure I have the setting switched on every new post, but, I could also get used to it