Great work, though could use some polish. I could not find the last flag, and wasn't sure what to do in 'Nocturne' world (beside listen to recordings). But otherwise I did see the ending.
- Increase movement speeds or make the worlds smaller. It takes far too long to get anywhere.
- Button to quickly leave a painting world (instead of returning to menu). Allowing player to quickly leave after getting secret piece, or escape if they encounter bug.
- Add an indicator on the painting (in gallery world) telling player if they've "completed" it (Found all collectibles).
- Best to model the environment, instead of stretching primitives, so that UVs are good. You could consider using probuilder. Not recommended but the lazy solution is a triplanar shader (uses world coordinates instead of mesh UVs).
- Binoculars/Zoom button would useful for the large open worlds.
- English text needs proof reading, and English translations of the French text would be nice.
- Final boat ride is too slow.
- ISSUE: In 'Abstract World' player can jump on broken bridge to reach final platform.
- ISSUE: Performance in grassy areas is extremely poor. Especially in the 'Final World'
- BUG: Collecting final 'Piet's Wall' piece twice resulting in me have 6/5 piece, preventing me from placing the painting in 'Abstract World'. (Luckly was able to fix by decompiling your code to find out how you were saving, then modifying registry).
- BUG: Exiting game while in 'Red Corridor', then resuming game spawned me in the core (which I had not unlocked yet). Fortunately could escape by climbing stairs, this also allowed me to collect the secret piece.