So I’ve been waiting for Ubuntu Mate 18.04 to be released for RPI3B+ ever since 18.04 was launched. Now 8 months later, we’re not sure if this going to happen yet.
Are there any supported Ubuntu variants that have full support for RPI3B+? A simple search revealed nothing of the sort which is quite surprising given how prevalent the two platforms are (rpi3b+ & Ubuntu).
It depends what you mean by ‘supported’. This is a term that I often read, but it makes little sense to me.
The ‘official’ server image can be easily adapted https://wiki.ubuntu.com/ARM/RaspberryPi#Booting_the_official_Pi_2_image_on_the_Pi_3B.2F3B.2B- . You just add on the desktop of your choice. Though it’s probably a good idea to remove the cloud-image packages as they can slow boot time.
If you want to start from a clean install with your own user account then use the mini iso. This is a bit more involved on the pi AArch64 on Raspberry Pi 2 (rev 1.2), 3B, 3B+ , but mostly it is just copying and pasting instructions and not difficult.
If the above is too hard, then I made a xubuntu-core armhf image AArch64 on Raspberry Pi 2 (rev 1.2), 3B, 3B+ . This works out of the box on pi 2, 3B, 3B+. All packages used are from the official ubuntu repos.
Hope that helps!
Try 64-bit Debian using the MATE desktop. It is appropriate for anyone that uses Ubuntu MATE.
http://cdimage.ubuntu.com/releases/18.04/beta/
In this link you can find official Ubuntu image. The default user password is “ubuntu” but you must change in the first boot. I did not try to install Mate desktop on it.
I’m not proposing to build anything. I recommend to use prebuild official images of Ubuntu 18.04.1
And those prebuilt images are extremely buggy (see bug report). If they work it is by accident, not design.
I’m comfortable been the guinea pig 
… So I’ll try to add Mate desktop to the official pre-built image.