Comment 62 for bug 1767703

May be I was too rude in my previous comment.

But this is actually as simple as selecting the right mode while booting up your machine.
In ubuntu 14.04 and 16.04 the selection window ware coming while installation.
In ubuntu 18.04 you need to select it manually while booting up.

The process is explained here in a very simple manner.

https://abcsofubuntu.blogspot.com/2018/05/bootup-your-machine-from-bootable-usb-device-in-right-mode.html

Yes, this is a bug if you say so. Or, may be intentionally removal of a fetcher for some reason.