what format must i use to format micro sd cardfor use in slot on macbookpro 2015 using Monterey 12.3.1

Depends on the Micro SD Card Capacity ?

Depends on for what usage the user what to use the Micro SD Card for ?

Using Only Apple Computers ? A - HFS Journaled with GIID Partition Map

Using on Apple Computers and Microsoft Windows computer ? A - exFat for being able to Read and Written to by both computers and able to move Files larger that 4 GB in size.

Here you go: File system formats available in Disk Utility on Mac - Apple Support