Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Install the Multiplayer Play Mode package (com.unity.multiplayer.playmode)
3. Open the Project Settings window (Edit > Project Settings)
4. Open the "Playmode" tab in the Project Settings
5. Click the "+" button to create a new Player Tag
6. Enter "asd" as the name
7. Click the "Save" button
8. Repeat steps 5, 6, 7
9. Observe the Project Settings window

Actual results: No information or warning is shown when creating a Multiplayer Player Tag with a name that already exists

Expected results: An informational dialog/popup/warning is shown that a Player Tag with that name already exists is shown and the "Save" button is greyed out

Reproducible with versions: 6000.0.66f1, 6000.3.5f1, 6000.4.0b5, 6000.5.0a5

Tested on (OS): MacOS SIlicon Tahoe 26.2

Notes:

• Editor's Tag window shows an error when a tag is being created with a name that already exists and does not let the user create that tag