This rule in .procmailrc used to work to decode RFC2047-encoded Subject fields :

:0
* ^Subject:.*=\?
{
  :0 h
  S=| formail -cx Subject: | \
      perl -MEncode=from_to -pe 'from_to $_, "MIME-Header", "utf-8"'

  :0 fhw
  | formail -i "Subject: $S"
}

It fails now, producing an empty Subject: field.

Reproducible: Always

Steps to Reproduce:
1. add the rule showed above in .procmailrc ;
2. echo 'Subject: =?UTF-8?Q?Bonne_ann=C3=A9e_!?=' | procmail ;
3. a new message should show up in your mailbox, bearing the date 1/1/70.
Actual Results:  
The new message reads :

Old-Subject: =?UTF-8?Q?Bonne_ann=C3=A9e_!?=
Subject: 

Expected Results:  
It should have been :

Old-Subject: =?UTF-8?Q?Bonne_ann=C3=A9e_!?=
Subject: Bonne année !

The problem started in Fedora 37, around April 2023, I think.