Hi, this should not be a problem, as the connection of the hard drives is backwards compatible. Unfortunately, however, the performance will not correspond to that stated in the specifications, as the connection limits some things here.
To be sure, you can check the compatibility list at either Synology or Seagate.
Simply select your NAS model and the compatible hard drives will be displayed. Inserted at the bottom left:
https://www.synology.com/de-de...
https://www.seagate.com/de...