Just upgraded to MacOS 11.1 and this did not work.
I have been digging into this and I found that it starts to bring up a new window before it crashes.
Also, I have notice that some e-mails work and most don't. It happens on all my inboxes. At one point, I thought it had something to do with the weird TO: line in my e-mails. It looks like this: "my e-mail address My Name <my e-mail address>". Some e-mails don't show the TO: line in the display panel. Those seem to work. However, I'm finding some with the weird TO: line that work too. So that's not it.
In addition, the Junk and Trash mailboxes are no longer listed under favorites, They are all separate for each inbox now. I prefer to have junk and trash go to one corresponding mailbox, not 4 separate ones.