As an extension to the t_cose library I have added support for encryption to COSE with the HPKE-based key exchange. You can find the code here: laurencelundblade/t_cose#46
The draft that describes the functionality is here:
https://datatracker.ietf.org/doc/html/draft-ietf-suit-firmware-encryption-03
Are you planning to add encryption capabilities to the libcsuit library?