While this article does do a good job of illuminating the potential challenges, it's a bit frustrating that there's such scant discussion of solutions.
IMO, this problem has been solved pretty comprehensively by the TUF framework[1], which has a number of solid implementations[2][3]. Many of these implementations even have reliable third-party reviews, so should be pretty trustworthy.
For a solution geared more towards the automotive use-case involving multiple vendors, see Uptane[1], a customization of TUF. The IETF is also working towards a standard for IoT updates[2] which I've found helpful.
[1]: https://uptane.github.io [2]: https://datatracker.ietf.org/wg/suit/documents/