You can use the title built-in function(only require MATLAB) to set a custom title — it is designed for graphics objects — instead of using insertObjectAnnotation, which directly adds a text-shaped annotation onto the image and returns the resulting RGB image array.
Additionally, if you want to customize the title position, you can also try the text built-in function(only require MATLAB) to place a custom title at specified coordinates.
Example:
figure;
t = tiledlayout(2,2);
% Tile 1
nexttile
plot(rand(1,20))
title('Your Title 1')
% Tile 2
nexttile
plot(rand(1,20))
title('Your Title 2')
% Tile 3
nexttile
plot(rand(1,20))
title('Your Title 3')
% Tile 4
nexttile
plot(rand(1,20))
title('Your Title 4')
title(t,"customized text here",FontSize=20,FontWeight="bold")
