minimum marks to get government MBBS college in 2021

Actually, this depends on your category, your domicile etc. You haven't mentioned all the details, and the cutoffs vary from state to other. When you're applying through Home state quota, the cutoffs is stay low but for through All India Quota, cutoff  is quite high.
It's a little bit difficult to predict the marks you need to get a seat in government medical college as the cutoffs keep changing every year depending upon various factors. But in general, depending upon last few years' trends, if you hails from general category then you should try to get at least around 550 marks in Neet, if you want to get a seat in a government medical college.