How to reproduce:
1. Create and open a new project
2. Go to Preferences > External Tools > External Script Editor and set it to Rider
3. Create and open a new project on a different Editor version
4. Go to Preferences > External Tools > External Script Editor and set it to VSCode
5. Open the first project and observe Preferences > External Tools > External Script Editor

Actual result: It is set to VSCode
Expected result: It keeps the External Script Editor set to Rider

Reproducible with: 6000.0.62f1, 6000.2.15f1, 6000.3.0f1, 6000.4.0a5, 6000.5.0a2

Reproducible on: macOS 26.1 Tahoe
Not reproducible on: no other environments tested

Note: This is a usability issue that reproduces in any Editor version and with any IDE