The AMTITLE command picks up drawing borders and title blocks from *.dwg files specifically reserved for this purpose.
Dwg files containing title blocks are in a folder named TitleDwg files containing borders are in a folder name Format. The path to the folder containing these folders are saved in the system editor key Acad/M
Paths
DwgTitle (Configuration file settings gef@Paths@DwgTitle). 
By default, the key points to C:\Users\Public\Public Documents\Autodesk\AutoCAD Mechanical 2022\Acadm\Gen\Dwg
| Entity | Path | 
|---|---|
| Drawing Borders | C:\Users\Public\Public Documents\Autodesk\AutoCAD Mechanical 2022\Acadm\Gen\Dwg\Title | 
| Title Blocks | C:\Users\Public\Public Documents\Autodesk\AutoCAD Mechanical 2022\Acadm\Gen\Dwg\Format |