Will buying a flat which generates $250 rent per month be a good decision?
Whether investing in real estate is a good decision or not depends on many things, including the current and future supply/demand for rental units in your particular area. There are many questions on this site about this topic, and another answer to this question which already addresses many risks associated with owning property (though there are also benefits to consider). I just want to focus on this point you raised:
I personally think yes, because rent adjusts with inflation and the rise in the price of the property is another benefit. Could this help me become financially independent in the long run since inflation is getting adjusted in it?
In my opinion, the fact that rental income general adjusts with 'inflation' is a hedge against some types of economic risk, not an absolute increase in value.
First, consider buying a house to live in, instead of to rent:
If you pay off your mortgage before your retire, then you have reduced your cost of accommodations to only utilities, property taxes, and repairs. This gives you a (relatively) known, fixed requirement of cash outflows. If the value of property goes up by the time you retire - it doesn't cost you anything extra, because you already own your house. If the value of property goes down by the time you retire, then you don't save anything, because you already own your house.
If you instead rent your whole life, and save money each month (instead of paying off a mortgage), then when you retire, you will have a larger amount of savings which you can use to pay your monthly rental costs each month. By the time you retire, your cost of accommodations will be the market price for rent at that time. If the value of property goes up by the time you retire - you will have to pay more on rent. If the value of property goes down by the time you retire, you will save money on rent. You will have larger savings, but your cash outflow will be a little bit less certain, because you don't know what the market price for rent will be.
You can see that, because you need to put a roof over your own head, just by existing you bear risk of the cost of property rising. So, buying your own home can be a hedge against that risk. This is called a 'natural hedge', where two competing risks can mitigate each-other just by existing. This doesn't mean buying a house is always the right thing to do, it is just one piece of the puzzle to comparing the two alternatives [see many other threads on buying vs renting on this site, or on google].
Now, consider buying a house to rent out to other people:
In the extreme scenario, assume that you do everything you can to buy as much property as possible. Maybe by the time you retire, you own a small apartment building with 11 units, where you live in one of them (as an example), and you have no other savings. Before, owning your own home was, among other pros and cons, a natural hedge against the risk of your own personal cost of accommodations going up. But now, the risk of your many rental units is far greater than the risk of your own personal accommodations. That is, if rent goes up by $100 after you retire, your rental income goes up by $1,000, and your personal cost of accommodations only goes up by $100. If rent goes down by $50 after you retire, your rental income goes down by $500, and your personal cost of accommodations only goes down by $50.
You can see that only investing in rental properties puts you at great risk of fluctuations in the rental market. This risk is larger than if you simply bought your own home, because at least in that case, you are guaranteeing your cost of accommodations, which you know you will need to pay one way or another. This is why most investment advice suggests that you diversify your investment portfolio. That means buying some stocks, some bonds, etc.. If you invest to heavily in a single thing, then you bear huge risks for that particular market. In the case of property, each investment is so large that you are often 'undiversified' if you invest heavily in it (you can't just buy a house $100 at a time, like you could a stock or bond).
Of course, my above examples are very simplified. I am only trying to suggest the underlying principle, not the full complexities of the real estate market. Note also that there are many types of investments which typically adjust with inflation / cost of living; real estate is only one of them.