Reproduction steps:
1. Ensure Android Support is installed for the Unity Editor version that you’re going to open the project with
2. Open the attached “IN-118465_MPM ADB Instance Error - FAV.zip“ project (link in the internal comments)
3. Make sure the “Android SDK Tools Installed with Unity (recommended)“ option is unchecked in Edit > Preferences… > External Tools
4. Open the Play Mode Scenarios window from Window > Multiplayer > Play Mode Scenarios (in newer versions: Window > Play Mode > Scenarios)
5. Select the "test" Play Mode Scenario
6. Expand the "Local Instances" list and try adding/removing an item to the list by pressing the “+” or ”-” button

Actual result: The “Local Instances” list does not show any of its items, and an ArgumentNullException is thrown in the Console
Expected result: A warning is displayed in the Console (just like when Android support is not installed for the Unity Editor at all), and the “Local Instances” list shows all of its items

Reproducible with: 1.5.0-exp.1 (6000.0.51f1), 1.6.3 (6000.0.65f1), 2.0.1 (6000.3.3f1, 6000.4.0b3, 6000.5.0a4)
Not reproducible with: 1.3.0-pre.2 (6000.0.3f1, 6000.0.22f1), 1.4.3 (6000.0.51f1)
Could not test with: 0.1.0 (2023.3.0a1), 1.2.2 (6000.0.3f1) (Play Mode Scenarios feature not available)

Reproducible on: Windows 11 Pro (25H2)
Not reproducible on: No other environment tested

Note: Reproducible in a new project

Actual error message:
“ArgumentNullException: Value cannot be null.
Parameter name: ADB instance cannot be null. Is Android SDK set?
<…>”

Expected warning message:
”Android SDK not set/found/installed/linked. Android instances will be disabled.”