Here's an update. I sent a bug report to Opera and received an acknowledgment e-mail saying that they could respond by e-mail but had noted the issue. I don't know whether they actually did anything about it, because I haven't been notified, but after a week of using a different browser and missing Opera, I tried again today and now find that I can print web pages from Opera, as before.

Since setting up a Lenovo Thinkpad T480, I find that I can no longer print web pages in Opera, as I was able to do with my previous PC. Pressing Ctrl-P results in the message "Print preview failed" and everything in the dialogue box is greyed out. What is causing this and how can I set up Opera so that it will print on a Canon Pixma TS 3420?
I've tried printing from MS Edge and this works fine, so It seems this is a specific Opera issue.

@leocg Aha! I've found that setting now, and it works. Thank you for making me aware of this!

@leocg I didn't know there was any such option. Where do I find that?

If the VPN is active, searching in DuckDuckGo is blocked. Whatever I search for, I get the following message:

This site can’t be reached
The webpage at https://duckduckgo.com/(search string) might be temporarily down or it may have moved permanently to a new web address.
ERR_TUNNEL_CONNECTION_FAILED

What's the point of a VPN if you can't browse while it is active?