I'm studying Mechanical Engineering, just an year left to graduate. Here in India, we have very low salary for mechanical engineers (even for those who are competent enough), it is around Rs. 12,000 to 25,000 ($150 to $300) monthly. Many of my seniors (graduated), have either lost hope for job or who went with IT industry has salary of about $500 monthly salary.

I want to join the IT industry (after looking into my competence for two days)
I wanted to join computer engineering before but couldn't.
I have interest and I'm willing to learn in IT.

I looked into becoming the full stack developer but the market seems to be getting saturated there as well.
Where do I start? Please advice?

There's nothing to advise; if you want to do it, then you're going to have to learn everything involved in a new specialty, period. Not sure why you 'couldn't join computer engineering', what you know already, what your skills are, etc. If you don't like working in IT (assuming, since you didn't START with IT), why do you think you're going to be happy working in it later on?

Mechanical engineers are in high demand, and if you actually know what you're doing, you can work pretty much anywhere with very good pay. No one here is going to be able to advise you on what path that YOU should choose in your life/career. That's up for you to decide. Want to know where to start? Read any of the job descriptions for any of these IT positions...they list the skills you need. So obviously if you want that job, you get those skills.

Out of curiosity, what was/is the barrier to learning computer engineering? The education tracks for computer engineering and mechanical engineering are very demanding but there is a small amount of overlap. That is something which might be capitalized upon and a fresh start made. Though a fresh start could set you back a painful amount of years + money.

One of the things generally lacking in IT / ICT is domain expertise. Thus you have an advantage with an actual mechanical engineering background. Therefore, I would recommend building on both your mechanical engineering education and combine that with your active computer interests. More details are needed there. Please tell more about your main interests in regards to what you want to use software for. Also, what did you like best about mechanical engineering?

What to learn next depends a lot on what you want to do (other than "full stack" or plain mechanical engineer). Ideally you can find an intersection between four sets: what you like to do, what you are good at, what is useful, and what you can get paid for. Less than ideally, you can find something in more than one set, but not all four.

If I were you, I would complete the mechanical engineering degree that you started. The grass isn't greener on the other side of the fence – it just looks that way to you right now.

"IT," e.g. "full-stack developer," is by now an extremely saturated market all over the world. There are simply too many people out there with almost the same skills and (lack of ...) experience. Mechanical engineers are much harder to find, and "the world runs on mechanisms and machinery."

You could use your mechanical engineering degree to get a position in a data center as a facilities engineer, from there you can move into building automation.

If you get a good grade on Mech Eng you should be able to transition (M.Sc. ?) into robotics, which is still a young industry.
Can you do/learn basic electronics? Ofc you'll also need SW skills as well - that's what makes it interesting.
There's a lot of variation on what balance of skills each position requires.

Yes I can learn electronics and have some basic SW skills. I'm also interested in Robotics and AI

there is your career path. pursue every opportunity that comes your way. a graduate degree will also help.