I’m honestly not sure where that’s coming from. If you select the Web search option, what search engine does it use? Can you also tell me what your default search engine for Brave is set to (Settings --> Search engines)?
Lastly, if you select text in other browsers and/or apps on your device, does the Amazon option appear there as well?
Web search option searches normally with the provider I want (Qwant). I see no option for Amazon in the settings. I haven’t seen that amazon pop up in any other apps when selecting text, I have no other browsers on this phone yet.
If that is the case, then there it must be the result of something on the system itself putting it there. Can you confirm whether or not you have the Amazon shopping app installed on your device?