Lost textures | Texture painting

I was working on my model for school and I almost finished it including the textures. After saving and reopening the file, all the textures I painted seem to have disappeared and appear as completely white instead. As you can see, if I hover over the file, the textures are still there but if I open the project, the textures are completely white. I've tried several ways to recover them but nothing worked yet.

Does anyone have an idea on how I can get these textures back or how I can prevent this from happening again?

Textures still visible on the mini display:

https://preview.redd.it/hk4i0q83gh3d1.png?width=1018&format=png&auto=webp&s=cc9b04d363072b264ead0b6e119b50a1c6b8ad21

Textures are showing up completely white:

https://preview.redd.it/74d6jo83gh3d1.png?width=1298&format=png&auto=webp&s=e96887badf6b89e5f214ee09005e8996b7ed3963

This is a different project on which my textures do work and I did in the same way.

https://preview.redd.it/bxl96o0pgh3d1.png?width=596&format=png&auto=webp&s=6e2dcae75f7d546eaa883c71019c395945a5c9f3