AutoCAD MEP 2024 toolset lets you specify the layer standard and layer key style to use in the current drawing. You can also specify that the selected layer standard and layer key style be imported automatically into new drawings.
The software includes several layer standards and several layer key styles in a layer standards drawing named AecbLayerStd.dwg. This drawing is located in ProgramData\Autodesk\MEP <version>\enu\Layers or in one of its subfolders, depending on the content you installed. The templates provided with the software are configured to load an appropriate AecbLayerStd drawing into new drawings that you create.