It won't boot, Have to resort to Recovery mode, so we need to know how to remove the driver.  Doesn't show in Driver Manager cause it's not loaded.

Don't know how to remove so Mint can redo it.  (helping my brother koolme2)

Might not be enough information here, especially for non-Mint people who might nevertheless have some useful suggestions. I'm aware of some problems with GNOME (at least with debian) and the AMD proprietary driver and they recommend to use the free driver instead.

https://wiki.debian.org/ATIProprietary

But there might be better Mint specific pages on this and if your goal is to remove the proprietary driver, you should be able to search for something like: how to uninstall radeon proprietary driver linux

How did the driver get installed in the first place?

If it was installed direct from the AMD download, then it might be possible to do this.

   sudo sh /usr/share/ati/fglrx-uninstall.sh --force

More info here:

https://mintguide.org/system/461-install-latest-amd-catalyst-driver-into-linux-mint.html

But if it was installed using the package manager, you should use the package manager to remove it.

It's not the driver and it's not Linux.

 IT did it again.
This time I did nothing except unplug the cable and plug in a HDMI one.
And it was happy.

Weirdly xrandr shows 3 choices, VGA, Displayport and HDMI, all show disconnected.

What?

Not sure if it's the DVI cable or not yet.....what do you think?

Maybe check on the Mint website & download the latest iso & re-install & see if it works without the AMD driver.   (Just guessing may not be at all helpful sorry.)