This is one and only one guide wich will show you how to really fix this problem. I've never noticed this issue on computers. Mostly this issue is only on laptops. There are 3 methods how to fix this: 1st Is use this guide. 2nd plug your notebook into TV or PC monitor with HDMI cable (it will force to render everything by GPU). 3rd method is disable hybrid mode (Most people know this as a MUX switch). All those 3 methods will fix this issue. If your notebook have mux switch, i recommend you use this option as it's one of the best and there is no need to continue in reading this guide.
1st step

Download this zip file[drive.google.com]

2nd step

extract all files into your Trackmania United (Nations) Forever folder

Steam users: C:\Program Files x86\Steam\steamapps\common\TrackMania United
Other Users: C:\Program Files x86\TrackMania United (if game isn't there installed you will probably have your game installed in your own made folder for games)

3rd step

Run dgVoodooCpl.exe and go into DirectX

4th step

On the right side change VRAM to 2048 MB and turn off in miscellanneous: dgVoodoo Watermark (do not change VRAM to 4096 otherwise your game will not launch!!!).

5th step

click Apply and run the game

Before: 264mb
After: 2054mb

For NVIDIA users don't forget to choose right graphics card for trackmania in NVIDIA Control Panel. I've found some, people wich said that this fix don't work for them. BUT FOR MOTHER OF GOD, IF YOU ARE SUCH ILLITERATE I DO NOT KNOW WHAT ARE YOU EVEN DOING ON COMPUTER and i don't expect, you are playing games on it. You will do better, when you go to library and take some book