Well, downloaded the wrong iso didn't I? I've got the right one and
all seems fine now. The iso mentioned in my last post may still have a
small problem though.

Sorry for the noise.

~/Downloads/Devuan $
sha256 -C isoSHA256SUMS devuan_chimaera_4.0.0_amd64_netinstall.iso
(SHA256) devuan_chimaera_4.0.0_amd64_netinstall.iso: OK

~/Downloads/Devuan $
gpg --verify isoSHA256SUMS
isoSHA256SUMS      isoSHA256SUMS.asc
gpg --verify isoSHA256SUMS.asc
gpg: assuming signed data in 'isoSHA256SUMS'
gpg: Signature made Thu Oct 14 14:01:09 2021 BST
gpg:                using RSA key E93D7167A4F5FA9E9FED497770285BA5CF280BA4
gpg: Good signature from "Ralph Ronnquist (rrq)
<ralph.ronnquist@???>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: E93D 7167 A4F5 FA9E 9FED  4977 7028 5BA5 CF28 0BA4