As Andreas said, the CU and GDR updates are different and cannot be mixed.
Previously, you could change between CU and GDR after installing a new SP; but with SPs now a thing of the past, you probably need to reinstall the Instance to change between them!
The latest GDR release for MSSQL 2017 is:
"KB4583456 - Description of the security update for SQL Server 2017 GDR: January 12, 2021"
which will upgrade your instance to version: 14.0.2037.2
Try this, should work for any 2017 Instance on the GDR stream.