If it's a platter-based hard drive, it could be fragmented.
Actually, if it's getting older, it might be time to think about replacing it with an SSD. I'd suggest something like a Samsung t7 "Shield".
Something else:
Is the drive that you're using NOW the ONLY drive that the data is stored on?
If so, your data "is in danger" without a backup.
You can't trust important data to only one drive. If something goes wrong...
Another excuse to buy that SSD!