the change to ubuntu-release-upgrader seems to prevent me upgrading an old raspberry pi, so its not just apple
An upgrade is not possible at this time
Due to a bug in shim, LP: #1928434, upgrades are not currently safe for your hardware.
Once that bug has been resolved you will be able to upgrade to the next release of Ubuntu.
the change to ubuntu- release- upgrader seems to prevent me upgrading an old raspberry pi, so its not just apple
An upgrade is not possible at this time
Due to a bug in shim, LP: #1928434, upgrades are not currently safe
for your hardware.
Once that bug has been resolved you will be able to upgrade to the
next release of Ubuntu.