This is how I got rid of the micro-stuttering in TT3. I mean those very short lags when you steer fast from left to right and repeat... Like some loading in the background from the stoneage.
While TT3 still has a FPS cap of 120 (minus 4 fps caused from the 'ultra' LLM), at least the micro stutters are gone for me.

My (short) Specs:
NVIDIA RTX 4090 (Driver: 536.23), LG 38GN950-B (G-Sync enabled), 4800x2000 (24:10), Samsung 980Pro @PCIe4.

1. Open the Nvidia control panel
1.1 Go to '3D Settings'
1.2 Open the 'Program Settings' tab
1.3 Add TT3.exe
2. Set everything as shown in the following two screenshots:
2.1 Low Latency Mode: Ultra
2.2 Max Frame Rate: 116
2.3 Vertycal Sync: On
2.4 And don't forget to hit apply!
3. Start TT3
3.1 Go to 'Graphics Settings' enable Fullscreen and set V-Sync to 60fps

PS: I don't know exactly why this fixed the stuttering, but as soon as I change any of the mentioned settings the irregular short stutters are back.

As you can see from the frametime graph (first line), on 'ultra' it's buttery smooth without any spikes.
4. Now, enjoy TT3 without micro-stuttering. Hopefully!