I need to combin 3 partitions into one should I reformat each partion to APFS on mac OS13.5

Depends on where they are. You can only merge free space into the immediately preceding partition. You must delete the partition you wish to merge, then drag the size handle at the end of the preceding partition around into the free space.

Partition a physical disk in Disk Utility on Mac - Apple Support

If you don’t care about the data in the first partition, it is easier to erase the entire disk.

To get Full Usage of the drive capacity >>

Erase and reformat a storage device in Disk Utility on Mac

File formats available >>

File system formats available in Disk Utility on Mac

Welcome and pleased it has answered your question fully

FWIW, APFS uses containers (what were called partitions with HFS+). Within those containers, you can have one or more volumes ... similar to what you could do with HFS+

Depending on how an external drive came formatted from the factory would dictate what scheme they used:

• Those "dedicated" for Mac, typically are formatted with a single HFS partition w/ a single volume. I've yet to see them come formatted for APFS.
• Those "dedicated" for Windows are typically formatted for with a single NTFS partition.
• Those that can be used by either, are formatted as either FAT32 or ExFAT.

What seems to have become more common recently is manufacturers are now pre-formatting their drives with more than one partition. Typically, one is quite small in size, contains one or more apps, and in a number of cases these small partitions cannot be erased. WD is one manufacturer that does this with their My Passport line.