I have a PixelBook and PixelBook Go and I will be sorry when they go end of life also. I would still be rocking my Chromebook Pixel LS if it was supported as the hardware is fine. I was really disappointed when Gogle dropped development of the Pixelbook. The HP Dragonfly Pro is supposed to fill the gap but it is not a 2 in 1 device like the original Pixelbook and availability outside the U.S. seems to be an issue. I know here in Canada HP does not have it available and they have put restrictions on U.S. sellers that they can't ship it to Canada. Boo HP Canada!
Hey @woozy there are lots of Chromeboxs available that would be perfect for him, I'm attaching a link for one below. I moved my late eighty-year-old Dad over to a Chromebox years ago when he was alive and it was the best move we made. He was able to operate it easily and the maintenance required by me went to just about zero. You need very basic specs for him, likely an i3 processor and 8 GB of RAM. He can use his existing monitor, keyboard, mouse and speakers. No need for antivirus and the updates will happen in the background and appear when he boots up.
As @kemtue suggested, downloading ChromeOS Flex will give you the OS you can install on a PC for testing. The advantage of an actual Chrome device is it will also run a lot of Android applications which ChromeOS Flex won't
Here is a YouTube video that might be helpful: https://www.youtube.com/watch?v=aiyxnrDbU0s