important emails not showing up in Mail

You bring back my old Comcast days from many moon ago.

Comcast will not be helpful. This may lay in their lap.

One thing I used to do was try to work with an individual at the business, to see if you can send THEM an email, and then they reply to you (to check you do get it - you likely will). This establishes you as doing some business with them, and they become "known" as far as your mail account goes, in Mail and with Comcast. I suspect too many people reported the bank long ago and it has gotten into the Junk list they have, which no one manages anymore over the years.

Check your mail settings that you don't have anyone sent to junk for a variety of reasons such as the email isn't sent TO you (they sent a bulk email etc).

People think of Mail Rules as only for keeping things out. You can also direct mail that's coming IN. You can set up a rule like this; I've used desktop Mail Rules for many years and have lots of luck keeping both things out and ensuring I see important things.

In Mail >Settings:

From > Ends with > @yourbank.com

Move Message: (Apple ID mailbox) Inbox.

Name the rule whatever you like "YourBank" and it will run in the background.

LAST thing is to wipe clean your junk mail and blocked addresses and strart from scratch. It's possible it got in the mix - I've done it myself. Again, from your desktop, open Mail, then to Settings>Junk Mail and Settings >Rules