WD HD (intel) won't open password unlocker on new Mac mini (M2)
my old external HD (2016) will not unlock on new Mac mini (M2)
In that case you will need to contact Western Digital for an answer: Contact a third-party vendor - Apple Support.
You do not need any third party products to password-protect external disks on Macs. Refer to Encrypt and protect a storage device with a password in Disk Utility on Mac - Apple Support.