Data show one value why all values not displying?

I understand that you are not receiving the full output of fid. since you are not storing the output of fid in an array or vector. In each iteration fid will store a new calculated value. To store the value you have to use you can use indexing to save those values. Refer the following code :

% Define the number of states
D = 15;
% Initialize the annihilation and creation matrices
aannihilation_a = zeros(D);
creation_a = zeros(D);
aannihilation_b = zeros(D);
creation_b = zeros(D);
% Fill the off-diagonal elements of the annihilation and creation matrices
for k = 1:D-1
aannihilation_a(k,k+1) = sqrt(k);
creation_a(k+1,k) = sqrt(k);
aannihilation_b(k,k+1) = sqrt(k);
creation_b(k+1,k) = sqrt(k);
end
% Create the composite annihilation and creation operators
a1 = kron(aannihilation_a,aannihilation_b);
a2 = kron(creation_a,creation_b);
a3 = a1 - a2;
% Define the range of values for the parameter r
r_range = [0.01:0.01:0.10];
% Loop over each value of r in the range
i = 1;  % to save from 1st index
for r = r_range
% Define the time evolution operator
u = exp(r*a3);
% Define the identity operator and the initial and final states
I = eye(D);
n = 10;
ket_0 = zeros(D, 1);
ket_0(1) = 1;
ket_1 = zeros(D, 1);
ket_1(2) = 1;
ket_n = zeros(D, 1);
ket_n(n+1) = 1;
bra_0 = ones(1, D);
bra_0(2:end) = 0;
bra_n_minus_1 = zeros(1, D);
bra_n_minus_1(n) = 1;
% Calculate the final state after time evolution
psi_ket = kron(I,bra_0)*u*kron(ket_n,ket_1);
psi_bra = psi_ket';
p = psi_bra*psi_ket;
psi_prime = psi_ket/sqrt(p);
% Calculate the fidelity between the final state and the target state
fid(i) = abs(bra_n_minus_1*psi_prime).^2;  % store values 
% Plot the fidelity as a function of r
plot(fid(i),r,'r*');
i = i+1;
hold on
end
% Set axis labels and legend
title('Fidelity vs r','fontsize',14);
xlabel('Fidelity','fontsize',14);
ylabel('r','fontsize',14);
grid on;