You may have to boot into Mojave and mount EFI partition you want clover on then run installer package
I suggest you clone your working clover EFI to EFI partition that your are trying to use to boot Catalina.
Then Update per my guide
Since I have one NVMe SSD for macOS (Catalina, and Mojave) and one NVMe SSD for Windows 10
I use my installer USB (Catalina and Mojave) to test newest clover first before updating EFI on macOS SSD
This also keeps Clover on USB drive updated as well
See my guide for updating clover, it prevents you from messing up your working clover install until you know the new version is configured for your system and works