Ubuntu – How to try Ubuntu 18.04 Live Server

I downloaded an Ubuntu 18.04 Live Server ISO.

I burned it onto a DVD-RW.
I can boot from that DVD-RW.
I press "tab" while booting as described here: If you act quickly enough, hitting the TAB key you will bring up the boot menu where you can choose to simply just try Ubuntu without installation. (Also described here.)

However, it doesn't show "Try Ubuntu." It only shows

• Install Ubuntu Server
• Check disc for defects
• Test memory
• Boot from first hard disk

and F6 "Other Options" doesn't show "Try" either.

How do I "Try" without installing? In fact, I want to boot, fix this damn bug, then boot from disk.

I looked at this page to debug, but a lot of it is about whether the DVD will boot at all. It boots, but doesn't offer the option I want.