Packages are broken

Question

Almost any time I try to use packages, they fail for one reason or another. I did manage to install a package some time last year (2020) but not since.

The marmalade-repo.org has had a bad certificate for years (expired 2017 I think) so I commented it out; my .emacs now says:

(require 'package)
(setq package-enable-at-startup nil)

(add-to-list 'package-archives
     '("gnu" . "https://elpa.gnu.org/packages/"))
(add-to-list 'package-archives
     '("melpa" . "https://melpa.org/packages/"))
;(add-to-list 'package-archives
;    '("marmalade" . "http://marmalade-repo.org/packages/"))

But any attempt at package-list-packages get the error:

Failed to download ‘melpa’ archive.
Failed to download ‘gnu’ archive.
Contacting host: elpa.gnu.org:80
Saving file /home/peter/.emacs.d/elpa/archives/gnu/archive-contents...
Wrote /home/peter/.emacs.d/elpa/archives/gnu/archive-contents
cond: Invalid version list ‘(8 6 -4)’

I'm obviously Doin' It Wrong™ but I don't understand where. Is there a way to make packages work again? Is there something I can do to help?