For thermal mass flow meter, Can it measure very small flow / low flow rate?

Yes, thermal mass flow meters are especially good at measuring very small and low flow rates of gas.
This is one of the biggest advantages of thermal mass flow meters compared with other types.
Excellent low-flow performanceThey can measure extremely low gas velocity and tiny flow rates that many other flow meters (such as turbine, vortex, or Coriolis) cannot detect stably.
Wide turndown ratioTypical turndown can reach 50:1, 100:1 or even higher, so it works well from very low flow up to full scale.
Measurement principleThermal type detects the heat transfer caused by gas flow, so it is sensitive to low flow and does not require a high minimum flow rate.
LimitationIt only applies to clean, dry gases.Liquid, moisture, oil, or dust will affect low-flow measurement.