How to reproduce:
1. Open the “PrefabVariantOnValidate.zip“ project
2. Open the “Prefab” and “Prefab Variant” in Notepad
3. Observe that there are no mentions of “m_serializedGuid“ in any file
4. Select the “Prefab” in the Project tab
5. Add the “Prefab Guid“ Script Component in the Inspector
6. Select the “Prefab Variant” in the Project tab and observe that there is a “Prefab Guid“ Script Component attached, and the GUIDs are different on both the “Prefab” and the “Prefab Variant”
7. Save the changes, and search for “m_serializedGuid“ in the opened Notepad for both the Prefab and the Variant

Actual result: Prefab has a serialized property “m_serializedGuid”, while the Prefab Variant does not
Expected result: Both the Prefab and its Variant have the “m_serializedGuid” serialized properties

Reproducible in: 2023.1.0a1, 6000.0.68f1, 6000.3.9f1, 6000.4.0b9, 6000.5.0a7

Reproduced on: Windows 11 Pro (25H2)
Not reproduced on: No other environment tested

Notes:
- If any manual change is made to the Variant after step 5, the “m_serializedGuid“ will be shown in the Notepad as a modification, and only then
- If any change is made to the Variant, the Guid string field can be reverted, and if reverted, it will return to the value of the parent Prefab