When logged out of Roblox, you still have options to follow and block users. Doing so will just prompt a error message under the avatar headshot;
“Unable to follow user.”
“Unable to block user. You may have blocked too many people.”
Expected behavior
Blocking and following options should either not be visible when unauthenticated, should redirect to the login page, or should prompt that the specific action requires you to Login to Roblox (similar to favoriting a game while unauthenticated)