Huh. The only thing I'm finding is (in Android's Settings) > Google > Search and Voice Input ... though as I've never installed Edge it may be that there's something added to Apps > (click the gear/cog icon at the top).
Though under Apps as well the 3 dot menu includes "Reset app preferences". Probably resets all default apps (hence may be overkill) but that ought to include search preferences.
I received a reply form Opera on my bug report.
The bug is confirmed. It was an unintended side effect from another change.
The solution is already implemented in the Chromium code and will be shipped in a future chromium release.
Opera, thanks for the prompt and clear reply.
I was aware of the thread you pointed to. According to me that was however a different issue unrelated to the fact that for me it only occured in a local testenvironment.