The only truly portable driver is a folder containing .inf , .sys , and .cat files. If you see a .exe larger than 20MB, it is not a portable driver; it is an installer.
Use the Win8.1 folder inside the portable pack. Note that Microsoft stopped signing drivers for 8.1 in 2023. You will need to disable integrity checks. realtek 8811cu wireless lan 80211ac usb nic update portable
The version number is critical. As of late 2024 / early 2025, these are the stable portable generations: The only truly portable driver is a folder containing