In the following forum thread from 2021 Jikstra says it should probably be easy to get the release script to upload a checksum.txt with checksums of all the uploaded files:
And then to simply sign the checksum.txt and upload the signature shouldn’t be hard I would think (but there could be difficulties involved which I don’t understand).
Compared to all the work writing and testing the Delta Chat code, I imagine that signing a checksum.txt file would be pretty quick and straight forward, and it would give many users more confidence that they downloaded the right code.