[type0]

> A MacBook from 2015 can't run any OS newer than Big Sur

It can, Ubuntu runs just fine on it

[josephcsible]

You're right, I should have been more precise. But you still won't get security updates to firmware anymore that way.

[rokkitmensch]

If this is your personal threat model, I commend you on an exciting life well-lived that appears to entail sophisticated personal protection of the GPG keys and Bitcoin you need to run your business empire securely.