Please read and follow If Mail unexpectedly quits when viewing certain messages - Apple Support.
The idea is to be able to open Mail without it crashing, and with no email message selected. If you can do that, then rebuild that Mailbox, or all Mailboxes, according to Rebuild mailboxes in Mail on Mac - Apple Support.
Needless to say, if you are using any non-Apple "anti-virus", "cleaning", or "Internet security" junk, anything at all in that broad category of useless garbage, don't. A lot of things won't work if you do.