Never

older devices probably never going to get the os update.

And say, tomorrow Samsung launches another device with more features than M30s and less price. Anyone who will buy M30s will say the same thing. It's about buying a best phone available at one time. Nobody knows what will be launched in future.

J7 prime 2 has the pie update not J7 prime. older devices like j7 prime, j7 max, most of the on series are probably not getting the update

Probably never. Older device may not get the Pie or future Os update. We can hope for the best though.