Was just about to concur and say this is still a horrible problem, but I thought I better check for updates first.

Problem fixed!

In the radical new "Opera One" (version 100.0.4815.76 running on macOS 13.4.1) I can't reproduce the raise-background-window behaviour. Phew, what a relief!

Perfect! I used "[{title}]({url})'" as the item format and "\n" as the delimiter for a custom format and have exactly the Markdown tab export I was after. Installed, configured and ran like a dream. Thanks.