Is the chat encrypted (i.e. has an avatar that is not 
)? Is there an error when you try to send the message?
It seems like your contact added non-standard Kyber encryption key. This is a GnuPG-only extension (so-called “LibrePGP”) and is not supported in rPGP. If there is only such encryption key available for the contact, then we cannot encrypt the message.
The easiest fix to all these problems is likely for your contact to stop using non-standard keys. But nevertheless, we should be able to decrypt messages sent to us, this is a bug that Delta Chat needs to fix in any case.