It is a common issue that Mac can't recognize the external hard drive encrypted with BitLocker given that BitLocker is not supported by macOS.
No matter whether the external drive is formatted with NTFS or exFAT on Windows, as long as the drive is encrypted with BitLocker Drive Encryption, you can not read and write the BitLocker-encrypted drive on Mac by default.
If you want to use the external hard drive on a Mac, you can turn off BitLocker first. Or, you can try BitLocker for Mac, the third-party software that can help you unlock and read-write BitLocker encrypted hard drives on Mac easily and securely. Among them, iBoysoft BitLocker for Mac is a good choice for you.
If you choose to disable the BitLocker on the HDD and access it on Mac, you'd better formatted it with a file system that is compatible with both Windows and macOS such as exFAT and FAT32, if the file system is NTFS, you can only read but can't write to it on Mac.
Even if the HDD is an NTFS drive and encrypted with BitLocker, you can use iBoysoft BitLocker for Mac to easily access the drive on your Mac. You don't need to erase the drive on Windows. It's the best solution you can try.
