Installing on Ubuntu 21.04

I have created a USB stick with the 2.8 installation files on it from the ISO. I can run 2.8 live from the stick just fine. If I try either the Install or Graphic Install option, when I get to the section for identifying a CD-ROM drive the installation has to be aborted. I do not have a CD drive in the system. I have tried a USB CD-ROM drive with a DVD in it with the installation files on it, but it is not recognized by the system.
UEFI is disabled. BIOS set to boot from USB first. I have created DVDs from both Rufus and the Windows ISO burner app.
Is is not possible to install from the USB stick?

I had no problems installing it on two different PCs. However, each one does have a CD/DVD drive.

I don't recall having to specify a CD/DVD drive, probably because one was already installed on my systems.

I suppose that you could borrow or buy a USB CD/DVD drive. They go for about $25 on Amazon.

I did attach a USB CD/DVD burner to the system and it was not recognized.

I have an old Dell 755 here and I am in the process of downloading Ubuntu 32 bit for it. I had some issues with the old beast, no HDD, but I found one, and the memory had to be reseated to get it to boot.

I had tried LXLE but it wouldn't boot. We'll see what Ubuntu Mate does...

Back to your problem, Does your PC see the CD/DVD in BIOS? And what version of Linux are you trying to install? Try installing a different version.

Meanwhile I will try to get Ubuntu going on my beater box PC.

Win32diskimager is your friend for bootable USB from Windows. Try using that.

So no surprises here, Linux installed without needing the CD/DVD drive to be connected.