How can I cause email from a certain source to come to the inbox instead of junk?

You might try creating a rule in the Mail app that will intercept the mail and route it properly.

Also, anytime mail from that sender arrives in the junk mailbox, right-click and move the message to the inbox.

Another option that may help would be to create a card for that sender in your Contacts app.

Use rules to manage emails you receive in Mail on Mac - Apple Support