Normally load Ubuntu via the iso directly as iLO virtual media, no issues with 20.04. Run the latest SPP to update the server and reset the server bios to defaults before running it.
Check if the USB key is working and is bootable on another system.
If it is working, then check if the USB ports are enabled. Refer to section "Setting USB Control" of the "UEFI System Utilities User Guide for HPE ProLiant Gen10, Proliant Gen10 Plus Servers and HPE Synergy".
If the USB ports are enabled, check if the ports work otherwise by connecting USB keyboard or mouse.
If the ports work then check if the "USB Boot Support" on the server is enabled.
Intelligent Provisioning does not support Ubuntu. F10
IP Supported OS include Windows Server (ISO only, not USB or network), esxi (HPE custom image), SLES, RHEL, and ClearOS.