Deleted Windows Through DiskUtility, 100GB in "Free Space", Unable to Combine to Main Partition
Solution 1:
If you are using High Sierra and APFS. Try this.
Below command to find the list of Drives.
diskutil list
run this to retrieve the the free space.
diskutil apfs resizeContainer disk0s2 0
Now your unused free space will be added to your existing hard disk as a single partition.