Google Apps for Domains used to have a catch-all feature. Now the docs say:

If you’re using another G Suite edition, the Email routing setting with the Route to catch-all address control is no longer supported. Instead, you use the Routing setting to configure catch-all addresses and routing.

but they don't actually have any instructions on how to do it.

Specifically I want to replicate the old behavior which is that if someone sends a message to [email protected] it gets forwarded to [email protected] in such a way that [email protected] can setup accounts in Gmail and can reply to the messages as [email protected].

If I check my legacy Google Apps for Your Domain emails and check the headers of a message sent to [email protected] I see absolutely nothing in the header that suggests it was forwarded to [email protected] and yet the mails show up in the inbox for [email protected]. This is important because when I reply, if I've added the [email protected] to my accounts under Settings>Accounts->Send Mail As... then I'm able to reply as [email protected] and not as [email protected]. For this to continue to work I assume the mail still has to be marked as to: [email protected] and not to: [email protected].