Please follow the below steps to install Built-In/URP version:
1, Copy Built-In.unitypackage or URP.unitypackage to some where outside your project,
2, Remove everything in 'Assets/SoftKitty/MasterCharacterCreator' folder except the following folders from your Built-In/URP project:
"ArtSource"
"Documentation"
"Scripts"
"Textures"
3, Import the Built-In.unitypackage or URP.unitypackage you just copied.