Follow
warning to #neomutt users upgrading to #debian #Bullseye: the "mutt" package became "neomutt" & the original #mutt took on the pkg name "mutt". So if you inadvertently install mutt, you'll run into problems like mutt using the variable smime_self_encrypt while neomutt names it smime_encrypt_self. And /usr/share/doc/muut/NEWS.Debian does not mention this.
Reminds me of a flemish commune that chose a different distance from the curb for their sidewalk, and even refused to make the sidewalk match up to the existing sidewalk at the Wallonia border, so everyone crossing the city boarder has to go across grass to get back on the sidewalk.