Am I eligible to get admission in MBM Engineering College, Jodhpur with a rank of 86687 in JEE Mains and 81.6% in class 12th?

With an REAP MBC category rank of 19, you have a very high chance of getting the Mining Engineering branch at MBM Jodhpur. MBM does offer Mining, and seats in this branch generally don't fill up as fast as core branches like CS or ECE. Your rank is excellent for MBC, so you should get it comfortably

It is unlikely to get admission in MBM Engineering College for BTech CSE with 72 percentile, CRL of 415565 and category rank of 27783 in JEE Main

With 94 percentile and 76% boards, you're above MBM Jodhpur's general-category CSE cutoff (~85–90 percentile). You meet eligibility criteria (50% in 12th) and should receive a seat in CSE through REAP counseling.

If your category is OBC, and gen, then it is not possible, but if you belong to sc/st, then there is some chance to get civil.

Noramlly, with these percentile you can easily get ECE, but I am not sure about other state cutoffs.