I’ve been unsuccessful in my attempts (three attempts to date) at creating a bootable DVD using the online iso of Ubuntu Mate 18.04.3 (Bionic) 32-bit version, which I downloaded from https://ubuntu-mate.org/download/).
I used two different computers in my attempts at creating a bootable DVD.
First, on a Windows 7 machine, I downloaded the iso for Ubuntu Mate 32-bit version using uTorrent, and then I burned that iso to a DVD using the Windows-bundled default disk burner application. When I tried booting a Lenovo notebook from the resultant DVD, the boot process got stuck in some kind of endless loop, with code-text scrolling rapidly and endlessly on the screen. Secondly, using the same computer, the same Windows OS, the Rufus USB flash-drive-writer, and the same downloaded-iso for Ubuntu Mate 32-bit version as before, I burned the iso onto a USB stick, which then I found to be unbootable into the same Lenovo notebook. The error message (which I didn’t write down) specified some files that were deemed missing. Thirdly, and in contrast, I performed an experiment, in which I succeeded in creating a bootable USB stick using the iso of Lubuntu 32-bit version (not Ubuntu Mate 32-bit version), which I burned to a USB stick using the Rufus application. However, I need a bootable DVD for Ubuntu Mate 32-bit version.
Next, on an Lubuntu machine, I downloaded the online iso for Ubuntu Mate 32-bit version again - this time using Transmission, and then I burned the new iso onto two DVDs using different disk writers, Xfburn and k3b. I found both of those resultant DVDs to be unbootable too. I don’t have another available USB stick, otherwise next I might have tried making a bootable USB stick using the Ubuntu Mate iso - but anyway I want a bootable DVD.