If you want to format an external hard drive for both macOS and Windows, you can choose either exFAT or FAT32 as the file system. In this way, you can fully access the drive on both Mac and Windows PC in read-write mode.
Have you checked the file system of the G-Raid drives on your Mac already? Before you proceed to format the external hard drive for Mac and PC, it is necessary to have a look at the drive format. Open the Disk Utility, click View > Show All Devices, select the target external drive on the left list, and check the drive info on the right side.
If the drive is formatted as exFAT or FAT32, then you can directly use the drive on both Mac and PCs with full privilege. You can still reformat the drive if you want to thoroughly erase all contents on the drive. Perhaps, the drive format is NTFS if it is used for Windows, or APFS/Mac OS Extended for macOS, then the drive is compatible with only one platform.
NTFS drive is read-only on Mac, and APFS is not writable on Windows PC. There are third-party tools that enable you to read and write NTFS on Mac such as iBoysof NTFS for Mac, there are also APFS drivers for Windows. With such software, you don't need to format the drive and can gain full read-write access to the drive.
If there are no important files on the drive, then you don't need third-party software to make the Windows-exclusive or macOS-exclusive drive work with both platforms, you can directly reformat it on your Mac and choose either exFAT or FAT32.