More detail on the problem.
after starting remote-viewer --debug, I get
(remote-viewer.exe:18308): virt-viewer-DEBUG: 11:45:30.594: New spice channel
000000000608B240 SpiceMainChannel 0
(remote-viewer.exe:18308): virt-viewer-DEBUG: 11:45:30.594: notebook show status
0000000003479130
(remote-viewer.exe:18308): Spice-WARNING **: 11:45:30.691:
../subprojects/spice-common/common/ssl_verify.c:444:openssl_verify: Error in certificate
chain verification: self signed certificate in certificate chain
(num=19:depth1:/C=US/O=xxxxxxxxxx.65101)
(remote-viewer.exe:18308): GSpice-WARNING **: 11:45:30.692: main-1:0: SSL_connect:
error:00000001:lib(0):func(0):reason(1)
(remote-viewer.exe:18308): virt-viewer-DEBUG: 11:45:30.693: Destroy SPICE channel
SpiceMainChannel 0
So it seems like there's some additional thing that needs telling to use the official
signed cert.
Any clues for me please?