The deb is busted since this release:
11.74 Setting up opera-stable (124.0.5705.42) ...
11.82 update-alternatives: error: alternative path /usr/bin/opera-stable doesn't exist
11.85 dpkg: error processing package opera-stable (--configure):
11.85 installed opera-stable package post-installation script subprocess returned error exit status 2
Tested on bookworm, Trixie, and Noble. Related to renaming the package but the deb contents do not contain that bin.
./bin
./bin/opera
The problem is specifically in your postinst in the deb:
EOF
chmod 755 /etc/cron.daily/opera-browser
# Run once now to add Opera's pgp key to apt's keyring
/etc/cron.daily/opera-browser > /dev/null 2>&1
update-alternatives --install /usr/bin/x-www-browser x-www-browser /usr/bin/opera-stable 120 \
--slave /usr/share/man/man1/x-www-browser.1.gz x-www-browser.1.gz /usr/share/man/man1/opera-stable.1.gz
update-alternatives --install /usr/bin/gnome-www-browser gnome-www-browser /usr/bin/opera-stable 120 \
--slave /usr/share/man/man1/gnome-www-browser.1.gz gnome-www-browser.1.gz /usr/share/man/man1/opera-stable.1.gz
;;
esac
Because the name was changed your deb build env looks like it templates that name into the post install hooks and every deb is failing now.