I have Seagate external drives. Who do I call to get the Kexts?

You cannot install Seagate kernel (kext) drivers into Big Sur, cause the operating system is on a signed, read-only partition. Even if could, you do not need to install vendor storage drivers to access their external drives, but you might need to reformat them if they are pre-formatted as Windows NTFS.

Sorry? Why do you think you need "kexts" to use your drives?

VikingOSX - Another user had success by downloading the WD software and she was able to mount her Seagate drives as well. This might be another option.

I hope this helps.

Paul