Hi,
Thanks for you reply.
I think I know where the issue was !
I tried to set the render settings to "High" but it did nothing in the viewport.
So I oppened the Settings panel and I noticed that the "Max texture size" was still in "1x1" even though I switched to "High" mode.
And I was, by default, in "Minimal", with no way to change the "Max texture size" (the setting is grayed out).
Going in "Medium" or "High" I can now set the "Max texture size" to 2048x2048 in the Settings panel and everything is working fine.

So I believe that the update did put the "Max texture size" to "1x1" by default on all render levels.
Anyway, problem solved. Thanks.