rotating a display

[djh]

I've just attached a display to a Pi 3B+. It's an old display attached
through a VGA-HDMI converter (no idea whether that's relevant!). I've
also attached a USB keyboard, though not yet a mouse.

I want to run the display in portrait mode. When I booted it came up
sideways (in landscape mode) as I expected. I started trying to use
xrandr via ssh to configure the display but haven't figured out how to
get it to work. Here's a sample of some output:

$ xrandr -display :0 --prop
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1280 x 1024, current 1280 x 1024, maximum 1280 x 1024
default connected 1280x1024+0+0 0mm x 0mm
	non-desktop: 0 
		supported: 0, 1
   1280x1024      0.00* 
$ xrandr -display :0 --output 'default' --rotate left
xrandr: output default cannot use rotation "left" reflection "none"

 I searched but haven't found any articles that explain my problem. So I
 thought I'd try lxrandr instead. That pops up a dialog box on screen
 saying "Unable to get monitor information!" and prints an error on the
 command line:

$ lxrandr --display :0
Can't open display

Somebody then told me how to rotate it 'the pi way', by
editing /boot/config.txt  That worked, but I'd like to understand why
the X way doesn't. I'm also unable to access the display remotely. From
my ssh session on the pi I can launch xeyes for example:

$ DISPLAY=:0 xeyes
^C  # terminate from keyboard

and I turned off access control:

$ DISPLAY=:0 xhost +
access control disabled, clients can connect from any host

But I can't connect to the pi from another host:

$ DISPLAY=RpiBplus:0 xeyes
Error: Can't open display: RpiBplus:0
$ ping RpiBplus
PING RpiBplus.fritz.box (192.168.1.22) 56(84) bytes of data.
64 bytes from RpiBplus.fritz.box (192.168.1.22): icmp_seq=1 ttl=64
time=0.314 ms
$ DISPLAY=192.168.1.22:0 xeyes
Error: Can't open display: 192.168.1.22:0

I'd appreciate any suggestion for places to look to explain this
mystery to me, or actual solutions of course :)

Thanks, Dave