How to reproduce:
1. Open the attached "IN-132255_My project.zip" project
2. Open the "SampleScene"
3. In the Hierarchy, select TestObject
4. In the Inspector, under "Unity Event Test (Script)" component, copy My Event ()
5. Under Button component, paste the copied event into On Click ()
6. Observe the On Click () event list

Actual result: The copied event does not get pasted into On Click ()
Expected result: The copied event gets pasted into On Click ()

Reproducible with: 2023.2.14f1, 6000.0.66f2, 6000.3.6f1, 6000.4.0b6, 6000.5.0a5
Could not test with: 2023.1.0a1, 2023.2.0a1 (Context menu doesn't show up, can't copy)

Reproducible on: Windows 11
Not reproducible on: No other environments tested

Note: Copying events from a custom script into another one or from a uGUI component into another uGUI component works as expected