Vivaldi on Android supports real custom search engines.

1. Open https://queye.co/ in Vivaldi.
2. Long-press the Queye search field.
3. Choose Add as Search Engine.
4. Review the name and nickname, and make it the default if Vivaldi offers that prompt.
5. If needed, go to Vivaldi menu > Settings > Search Engine > Standard Tab and select Queye.

You can also install the Queye Android app if you want a direct fallback.