I've also tried this code and it's also only giving me a peak at zero:
filename = 'Sample192.xlsx';
T = readtable(filename);
x = T{1:555201,1};
y = T{1:555201,2};
%
figure(1)
plot(x,y);
%
Y = fft(y);
Fs = 20000;
f = (0:length(Y)-1)/length(Y);
%
figure(2)
plot(x,abs(Y))
%
figure(3)
plot(f,abs(Y));
%
n = length(y);
fshift = (-n/2:n/2-1)*(Fs/n);
yshift = fftshift(Y);
%
figure(4)
plot(fshift,abs(yshift));
%