How can I merge primary APFS partition with other empty APFS partition?
If anyone still looking for answer.

Step 1: Delete the container

sudo diskutil apfs deleteContainer disk0s3


this will change the container to Apple_HFS Untitled                98.9 GB    disk0s3

Step 2: Erase the volume

sudo diskutil eraseVolume "Free Space" %noformat% /dev/disk0s3


Step 3: Resize the container

sudo diskutil apfs resizeContainer disk0s2 0