Your project looks visually pretty impressive. I really like the shadows and day/night lighting cycle.
Your level loading being based on bitmaps is pretty clever, but once you start relying on more than one bitmap, both of which need to correspond to each other (for locations of collision, etc.), it might make more sense to create a more custom level editing tool so that it's easier to specify some of the metadata required. Have you looked at all into that? I see you're already using Dear Imgui for parts of your code, that's something that could make such a tool easier to build.
I didn't see any source code download link. Is your code available somewhere? Based on the code visible in your video, it looks fairly readable, but like you said, some of your level loading code is a bit complicated.
Overall, looks good!