This message is usually associated with absence of disk or no boot sector. 1st make sure that the disk is visible/detected in BIOS settings.
If it is and it remains non-bootable, you probably did not install your newer Clover version with the suitable settings (legacy vs. UEFI for instance). You'll have to recover your installation through an alternative boot device, whether a USB key or an external USB disk for instance.
It dates back to Oct 2019 so it's a bit old now but here, you'll find details of Clover version and Clover settings that I used for Catalina on the Latitude E7250. Then you may look at my E7270 guide for Clover settings used to install more recent versions of Clover and macOS.
Recommended BIOS settings for the E7250 (and E7270) are available at the top of the E7xxx forum section.