Certain macs have fusion drive which is a mix of rotational and solid state drive. macOS can make it appear like one complete drive which Apple calls Fusion drive. If the drive is split we can see individual disks in Disk Utility. To fix the split drive boot into recovery by rebooting with holding Command + R. Next launch the Terminal. For Mojave or later Apple had made it fix using a single command. Note that this will erase all contents of the drive.

diskutil resetFusion

For previous version check Apple Support article. Below are the logs from running the command using Ventura installer.

diskutil resetFusion

Internally-located hardware disk devices known to the currently-running macOS:
Rotational                               (disk1)
Solid State                              (disk0)

Volumes exported by partitions or storage systems hosted on the above devices:
BOOTCAMP                                 (disk0s3)
jsloop                                   (disk1s1)
work                                     (disk1s2)

disk0 will be used as the "main" ("faster") device
disk1 will be used as the "secondary" ("larger") device

WARNING: All of the above will be erased
Do you want to continue? (Enter "Yes" to proceed to erase)

Force-unmounting all volumes on the chosen "main" ("faster") disk drive
Started on disk0
Finished on disk0
Force-unmounting all volumes on the chosen "secondary" ("larger") disk device
Started on disk1
Finished on disk1
Creating a new partition map on the "main" ("faster") disk device
Started on disk0
Unmounting disk
Creating the parition map
Waiting for partitions to activate
Finished on disk0
Partition disk0s2 will be the "main" ("faster") APFS Physical Store
Creating a new partition map on the "secondary" ("larger") disk device
Started on disk1
Unmounting disk
Creating the partition map
Waiting for partition to activate
Finished on disk1
Partition disk1s2 will be the "secondary" ("larger") APFS Physical Store
Creating an APFS Fusion Container importing two partitions
Started on disk0s2
Creating a new empty APFS Container
Unmounting Volumes
Switching disk0s2 to APFS
Switching disk1s2 to APFS
Creating APFS Container
FusionLC autodetect: regular Fusion
Created new APFS Container disk2
Finished on disk0s2
The new APFS Container is disk2
Adding a logical APFS Volume to APFS Container
Started on disk2
Preparing to add APFS Volume to APFS Container disk2
Creating APFS Volume
Created new APFS Volume disk2s1
Mounting APFS Volume
Setting volume permissions
Finished on disk2
The new APFS Volume exported by the APFS Container is disk2s1
Confirmed that your new volume "Macintosh HD" (disk2s1) is a Fusion Drive
Operation successful; you should now install macOS

I had done a clean install of Windows. I had to split the drive so that the Windows installer could recognize the partition. Now that I want to have macOS back, I need to merge the drives. Once done we can see a single Fusion Drive > Container disk2 > Macintosh HD from Disk Utility.

By default the APFS volume created is not case-sensitive. If we want case-sensitive volume, choose Macintosh HD and Erase. Choose APFS (Case-sensitive).