chip I re-downloaded the zip, checked again, and got the same results as you this time. No idea what went wrong there.
Whatever it was, the signature check stopped the device from being bricked. Good!
chip I tried again to install the update via adb, and again it failed. This time however I got error 61 which is something about a corrupted device. I did take notes, but they have been scribbled over by a toddler now and I can not read them.
If you do the sideload again I expect it will reproduce the message (which would be useful).
chip Anyhow, with a corrupted device I assume either something went wrong with the last update which is why this one won't install, or I have a hardware error in the storage. Either way I assume the only way to get back up to date is to fully reinstall Graphene OS again.
Likely, but not yet for sure. Is it possible to get the error message?