It immediately worked! An e-mail that was displaying HTML code properly displayed after rebuilding the In Box. It remains to be seen if this temporary fix will stick between openings of Mail.
On a Mac since 1984. Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
