According to the release notes, the Fa4 Firmware UPD would:
Audiophile components require precise software instructions to manage clock synchronization, power delivery, and digital-to-analog conversion loops. Firmware updates for the FA4 generally target three core areas: F.audio Fa4 Firmware UPD
Enhanced Bluetooth connectivity for both PC and Android, and more reliable performance when used as a USB DAC. According to the release notes, the Fa4 Firmware
Address reported issues where display colors or brightness may not be at optimal levels. System Performance: According to the release notes