FFT in 5G

Simply, It is because 3G and LTE have the same clock timing for multi technology handsets .

But in all resources about LTE physical layer, it is stated that sampling rate is 30.72Mhz = 2048 samples in 66.67micro-sec.

NR supports a maximum FFT size of 4,096, which is double that of LTE .

In comparison, 5G NR maximum carrier bandwidth is up to 100 MHz in frequency range 1 (FR1: 450 MHz to 6 GHz), or up to 400 MHz in frequency range 2 (FR2: 24.25 GHz to 52.6 GHz) that can be aggregated with a maximum bandwidth of 800 MHz.