You’re right that Mbed Studio uses PyOCD to flash the EVK-NINA-B1. On Windows, the Mbed Studio logs are stored in %HOME%\AppData\Local\Mbed Studio\mbed-studio.log, including any PyOCD errors.
For further help, could you email the log files to studio@mbed.com please?
pyocd.core.exceptions.ProbeError: STLink 48FF6D066578555529082167 is using an unsupported, older firmware version. Please update to the latest STLink firmware. Current version is V2J17M4, must be at least version v2J24.