@Jamesos1962
Hi, I never had this on my mobiles, so just guessing.
I would delete the password, if your remember it, and add it again at the next login.
I was able to set qwant as my defaulr on my Samsung Galaxy S10+. The installation there ist there for a while now.
Later, last year, I was not able to do the same on the Samsung Galaxy Tab S6. Now it ist also not possible on a fresh Samsung Galaxy S21 Ultra.
So it was there at some time and stayed on the oldest Installation or it has something to do with the device.
But I can confirm the option is there at least on one device. I am little dissapointed because Vivaldi announced a cooperation with qwant.
But if it is qwant or something else I want to use un the future: I voted for the custom search engine on android.
Same issue with a bunch of sites. Twitter for example, I don't use the app, I use the website, and Speedkey just plops itself over Vivaldi. The browser window does not resize to accommodate the keyboard, so I have to set the keyboard in hover mode and put it at the top. It would be nice if the browser was keyboard aware.