[UE5.6] Cannot find GameMode Blueprint derived from C++ class in Project Settings

[GuoRen]

Following the official " Code a First-Person Adventure Game" tutorial:

1. Created C++ class AdventureGameMode
2. Created Blueprint BP_AdventureGameMode derived from it
3. Went to Project Settings → Maps & Modes → Default GameMode
   https://dev.epicgames.com/documentation/en-us/unreal-engine/code-a-firstperson-adventure-game-in-unreal-engine

Problem:
BP_AdventureGameMode doesn’t appear in the dropdown
Why isn’t my Blueprint detected as a valid GameMode?