How does the HX711 circuit work?
The PNP transistor is used by the internal linear regulator. This provides a stable \$V_{DD}\$ and excitation voltage for the IC and bridge respectively.
The resistors R1 and R2 are used to set the feedback for the linear regulator.
Capacitors C1 and C2 are decoupling capacitors for the IC's power supply.
Capacitor C3 is decoupling for the internal bandgap reference.
Resistors R3, R4, and capacitor C4 form a differential low pass filter.