As far as I know at the moment all bezier curve-to-mesh operations using Geometry Nodes assume a bezier curve is 3D, and thus suffer from the same limitations that regular 3D bezier curves suffer in Blender. That is bevel on tight corners will look narrower than on linear parts.
Only workaround I know at the moment is using a Resample Curve node before Curve to Mesh with a very high frequency. Either set it to Length with a low value, or Count with a high value.
Obvious downsides are
- Unnecessarily high amount of redundant geometry added
- Rounded corners on tight angles rather than sharp angles.
- It actually just "hides" the issue under overlapping geometry
Beware that this workaround generates a lot of extra geometry and will invariably be heavy and resource intensive, which may lead to performance issues.
Another possibility for curves with straight segments only is to break the curve at each corner into separate splines before bevelling with Curve to Mesh. The downsides being the gaps that will appear at the seams and if the corners don't meet at 90° you wont get correct continuity.