UI-Minimalist dashboard unavailable after 2026.4.2 update

I updated to 2026.4.2 today and was greeted by a completely unknown “Overview” tab, and was unable to select (or find) my custom-coded Minimalist dashboard. I can’t find anything in the release notes about a breaking change, and 2026.4.1 worked fine. Have I found a bug or did I miss a critical change?