Reproduction steps:
1. Open the attached "PROJECTFILE" project
2. Open the “256 Nodes.shadergraph” and the “Empty Subgraph.shadersubgraph” files
3. In the “Empty Subgraph” Sub Graph Toolbar, click the Save Asset button
4. Click on the opened “256 Nodes” Shader Graph

Expected result: Unity Editor loads and displays the Shader Graph as fast as when opening a Shader Graph with a smaller amount of nodes
Actual result: Unity Editor loads and displays the Shader Graph after loading for several minutes

Reproducible with: 2021.3.30f1, 2022.3.10f1, 2023.1.15f1, 2023.2.0b11, 2023.3.0a7

Reproducible on: macOS 13.6 (M1 Max)
Not reproducible on: No other environment tested

Note: With version 2023.1.15f1 the Editor loads and displays the Shader Graph faster than the other mentioned versions