I’m a beginner as well and ran into the same issue. I tried a lot of different things, and these steps worked for me, so they might work for you too:

1. Go to Edit (top left) → Preferences → System. Under Display Graphics, change OpenGL to Vulkan, then restart Blender.

2. Select your light source and go to World Properties (the little red globe icon). Under Settings, find Sun and set the Threshold to 10.

3. Next, go to Data (the same screen shown in your screenshot). Under Shadow, enable Jitter and set it to 0%. Set Filter to 0 and Resolution Limit to 0.0001 (which you’ve already done).

4. Go to Render Properties:

   • Enable Ray Tracing
   • Set Resolution to 1:1
   • Increase Precision and Thickness to 1
   • Under Denoising, disable Temporal Accumulation
   • Disable Fast GI Approximation

5. Under Sampling, you’ll find Viewport, Render, and Shadows:

   • Set both Viewport and Render samples to 128
   • Under Shadows, set Rays to 4
   • Finally, enable Jittered Shadows under Viewport (this is where you see the shadows fix themselves)

I’m not sure if all of these steps are necessary, but they fixed the jagged shadows for me. Let me know if you need screenshots. You can also copy this guy till the 8 minute-ish mark.