Doppler processing eliminates clutter it doesn’t eliminate EMI, thermal noise, or atmospheric issues.
China’s 366 radar can detect 0.1 sq meter targets at 20km. It’s China’s most modern radar and it’s not close to 100km detection range for LO aircraft.
Play around with the radar range equation.
For a 100km detection range. 1 MW of output power, 30 dB antenna gain, 1Ghz Tx frequency, radar cross sectional area 0.1 m sq, minimum detection signal 0.005 nano watts.
On low power systems where you can have much lower internal emi, -100 dB (0.1 nano watts) is as low as you can get outdoors.