I've had this problem since the launch of Trackmania 2020 where there are no car shadows in any replay, the replay editor and therefore rendering.
There are a few threads that suggest fixes for this problem.
I've tried all of them to no avail. It seems that only a very small subset of players have had this issue continuously. The last one is a cloesd thread from the official forums but that does not solve the issue for me.
My GPU is a RTX 2080 (Latest Drivers) and all Settings but reflections are maxed out ingame.