I bet you are having the same problem I had when installing Catalina on this laptop. Try going back to UEFI, not legacy. In your clover drivers folder move the hfsplus.efi, and apfsdriverloader.efi files to the root of the flash drive. Now clover should show up. When it does go to the UEFI shell. most likely your flash drive will be fs0: . If it is type fs0: and. hit enter. Now type "dir" and hit enter, make sure the apfsdriverloader.efi is listed. Now type "load apfsdriverloader.efi" and hit enter. If you also need hfs, then do "load hfsplus.efi" and hit enter. Now type "exit" and hit enter. Now you should have the option to install. I never did find a way to automate this, so every time I restart, I have to load the driver manually. Hope that works for you!
Oh if you don't need afps, then just use vboxhfs.efi instead of hfsplus.efi, that will work without having to manually load it