Yeah, I poked around in the formats a bit and saw that it was obviously totally different from what your code was looking for (based on the Dev Tools Console output). Seemed really odd to me too that they just changed that, maybe it streamlines their serializer internally or something? So weird in particular to get rid of the version identifier though.
Oh, and to be clear I opened them in the beta only after checking my projects into git and making a manual backup as well. ;) Though with the bug in the last 2023 release I am pretty stuck since in 2023 release I can't import your extensions and in 2024 I can't open the projects with your editor. Not your fault at all though obviously. Just a silly situation is all.