Clover worked good for my Xeon E5440 on hp dx2810 with HS and Catalina, but it stuck on grey screen with frozen mouse when I tried Big Sur beta Installer.
I managed a Opencore BIOS USB which worked for HS and Catalina, but stuck at [EB][EXITBS] for Big Sur beta Installer with im144 and mp61 while it can deny im142 and mp31....
You can try it.
config.plist.oc063.775.im144.zip