Unity provides a tool for merging scene and prefab files called Unity YAMLMerge.

Recommended Reading:

• https://docs.unity3d.com/Manual/SmartMerge.html

• YamlMerge does not function properly with the new “Serialize Inline Mappings On One Line” Editor Setting. YamlMerge will always output inline mappings on two lines, as if this setting were disabled. ¹⁾