RenderTextures and Portals

[late osprey]

Hello everyone,
I don't know if i'm allowed to make a thread here, but i have an issue that i can't even understand.

I recently made a portal system, loosely based on what Brackeys did. The portal is a "door" on an other portal, which can then lead to an other... until the end with a null portal.

I got my project working on windows (unity 6.000.40f1) without any issues, but opening the project on debian somehow broke the RenderTexture system

here is the whole Portal class :

When the game starts, the custom shader's "_MainTex" stays white, as if no texture was assigned

however, the inspector says a RenderTexture was created, but its contents seem invalid