Getting the Opera Mini XAP to install on Windows 10 Mobile is entirely possible through and manual sideloading. However, due to broken security certificates and outdated proxy configurations, its utility as a daily web browser is highly limited. For the best web experience on your vintage Lumia or Windows phone, look toward native Windows 10 Mobile APPX files archived by the active homebrew community.

: Copy the XAP file to your phone's storage or SD card. Open the File Explorer app, locate the file, and tap it to initiate the installation.

Because Windows 10 Mobile includes a backward-compatibility layer, it can install and execute specific silverlight-based .xap application packages. However, you cannot simply tap a .xap file in the File Explorer to install it. You must use developer sideloading tools. Requirements for Installation

: Download and install the Windows Phone SDK 8.0 Lite or the full SDK. Also, ensure your computer has the .NET Framework 4.5 installed.

: Download a deployment tool such as WPV XAP Deployer or WPAppDeploy .

Opera Mini XAP for Windows 10 Mobile: How to Download, Install, and Make It Work