Fast forward to almost Feb 2026, I’ve been exploring the full Penpot project. It looks gorgeous. Congratulations on this work, I cannot wait for this to be a reality! Having worked on Development, UI/UX and Photography, I can confidently say your design ticks so many good, makes it approachable and friendly while preserving all the power-user features 
On the Darktable side, it looks like a migration to GTK4 is needed before start to properly revamp the UI. GTK3 to GTK4 does take some time. We’ll see how it goes: Gtk4 Migration - Progress · Issue #15920 · darktable-org/darktable · GitHub