Render Texture aspect change after turning off fullscreen with alt-tab

Hello,
I have a render texture used to render a portrait of my character. The gameObject with render texture is a child of the canvas (although it is not rendered into UI Image, but just texture). It works fine, both in fullscreen and windowed mode (Windows PC). But, when I change from fullscreen to windowed mode with ALT-TAB.

Please see attached screenshots. How to fix that?

Thank you in advance

Please help! Did no one encountered this issue? I am not sure if that’s a bug or just there should be a work around just for render textures.
Best!