iPad version update

If you have access to a full computer, like a Mac or Windows PC, try either using the Finder on a Mac that has the newest macOS Catalina installed OR with an older Mac with an older Mac OS, download and install the latest iTunes version ( or latest iTunes for Windows PC ), make sure the Mac or Windows PC is connected to the Internet, connect your iPad by the USB charge cable to the computer and let the iTunes application upgrade/update that 6th gen iPad model, using the iTunes Software Update feature, to its current, maximum iOS of iPadOS 14.3.

Best of Luck to You!

See this support article:--> If your iPhone, iPad or iPod touch won’t update

If the issue still persists, try to update your iPad connecting it to a computer running iTunes (Windows 10 PC) or iTunes/Finder (Mac).

Regards

Giulio