Use multiple apple IDs in messages / iMessage on BigSur
We have multiple apple IDs setup in Family sharing. We would like to have all of the phone numbers be available in the messages app when we use the Mac. Essentially, have the Mac logged into and allow any of the phone numbers send or receive messages on the Mac's messages app. Right now the only thing we can do is use the phone number associated with the apple ID that logged into the Mac.
We are on BigSur and the previous recommendations on Google regarding adding more accounts in messages do not appear to work as the accounts tab is missing in BigSur.
iMac Line (2012 and Later)