After importing subscriptions into an Unread Cloud account or Local account, how can I later add another subscription?

From a subscription list or article list, swipe the screen to the left and select Add Subscription from the resulting menu. This also works for Feedly accounts and Inoreader accounts.

For Feed Wrangler, Feedbin, and NewsBlur accounts, the procedure is similar. From a subscription list or article list, swipe the screen to the left, select Add from the resulting menu, and then select Add Subscription from the resulting submenu.

If using a hardware keyboard, you can add a subscription with command-shift-n.

I no longer see Settings, About, or Release Notes from the Home screen of Unread.

Settings is now available from the swipe left menu of the home screen, subscription lists, and article lists. Release notes, the About screen, and similar functionality that was available from the Home screen is now part of Settings.

Why does Sign in with Apple not offer to use a private email relay address for Unread Cloud?

Unread Cloud does not request or see your email address at all. Unread Cloud also does not request or see your name when creating or logging in to an account.