Am Fri, 12 Aug 2022 20:08:06 +0200 schrieb Ulrike Fischer:

> \Uchar"FFFD
> \bye
>
>
> errors with
>
> ! String contains an invalid utf-8 sequence.
> l.93 \Uchar"FFFD
>
>
> (^^^^fffd  works)

Addition: while ^^^^fffd directly works, \detokenize {^^^^fffd}
fails with the same error