communities on other servers aren’t automatically and easily available.

You may be aware but for others, on the main page you can change which communites are displayed. At the top, there is the option or Subscribed, Local, and All that's only a single click/tap. (I do personally think the default should be All)

• Subscribed shows you just the content from the communities you are following from any instance.
• Local shows you the content from the communities only from the instance you're currently viewing.
• All shows you posts from the communities of all the instances that are federated with the instance you're viewing from.

From the list of posts, you can then select a community from a different instance (these will have the community name with something like @example.ml at the end) which will bring you to that instance. From there, you can select the "Communities" option from the menu and it will show you all the communities that are hosted on that instance.