Some museums nowadays demonstrate
nowadays is in present. Therefore the verb should be in present tense.
Some museums nowadays demonstrated that museums are more likely to be entertainment along with educative, and this is determined by the modern methods of teaching,however
. There are also a classical type of museums in the meantime.
You have several grammar issues here. Try to write shorter sentences until you become very confident with grammer. Also limit one idea to one sentence. Dont have irrelevant ideas in between (see the part in bold which does not contribute to your other ideas). Also state your opinion in the introduction.
This is my suggestion for your introduction;
Some museums today are more focussed on providing entertainment to the visitors. While some people approve this trend, others believe that the main purpose of the museums, which is education, is lost when they try to entertain visitors. In my view, the museums need to educate people in an enjoyable manner.