If decryption fails due to a missing integrity check (MDC) then Kleopatra shows a "Force Decryption" button. This allows the user to ignore the missing integrity check and to force decryption with GnuPG.
I think this button should be removed. I think nowadays ignoring a missing integrity check on decryption is an absolute no-go. Therefore we shouldn't make it easy for people to shoot themselves in the foot. People who need to decrypt decades old data without MDC should use the command line. (We could show a hint in Kleopatra in case decryption fails because of missing MDC.)
I stumbled over this while looking into {T7784}.
Some background information: The button was added with {T4038}. It's only shown for legacy algorithms without MDC, i.e. if AES is used then decryption simply fails without more specific errors (see {T4402}).