Here's what I did in MATLAB R2025a to export the current figure in bmp format. However, I did not face any warnings.
fig = getframe(gcf); % Capture the current figure as an image
rgbImage = fig.cdata; % Extract the RGB image data
% Convert to indexed image with 256 colors
[indexedImage, cmap] = rgb2ind(rgbImage, 256);
% Save as BMP file
imwrite(indexedImage, cmap, 'myfigure.bmp', 'bmp');
If you still face the warning please attach a simplified code that can be executed to reproduce the warning.
