@bizarro Thanks, I've updated my table above! I also added 🚫 to a bunch of the entries, to help illustrate this is a more widespread problem than with just Swisscows.
It looks like suggest URLs exist but aren't supported by Vivaldi for 7 different engines I've added -- Yahoo, Google Play, Merriam-Webster Dictionary, Merriam-Webster Thesaurus, Reddit, Swisscows, and Wolfram|Alpha.