After years of community testing on forums like CrackBerry (now archived) and BBOS.org, the consensus for the best performing OS for the 9720 is:
With BlackBerry World’s servers having significantly reduced functionality, the primary method for better software acquisition is —transferring app files from a computer directly to the device. To do this effectively, users should follow a disciplined workflow:
After following this guide, you will have arguably the most stable version of BBOS 7.1 ever released. Will it run TikTok? No. Will it run WhatsApp? No (Meta killed support). Will it run Spotify? No.
Remove the battery for 30 seconds, reinsert it, and let the phone reboot. This hard resets the radio stack.