I'm not familiar with those devices in particular, but I wish vendors would take steps to make life easier for after-markt firmware developers especially once devices go EOL by doing things like proactively dropping a GPL tarball and giving people a way to disable secure boot locks on devices that have them.
(see "uv" option here https://fidoalliance.org/specs/fido-v2.0-ps-20190130/fido-cl... - the -sk key types in SSH are just a clever way of abusing the FIDO protocol to create a signing primitive)
With GPG it just works.