These days it is often contested how many genders is there. So my question is how many genders is there and is it unnatural for evolution to generate multiple genders.
Sex vs Gender
Sex is defined by the anatomy of an individual. The majority of people can safely be categorized as either male or female. There are exceptions and limit-cases of course such as intersex people for example.
Gender is a social construct. It is therefore not the role of a biologist but the role of a sociologist to address the details of the concept of gender. I am therefore not trained to discuss these points but I will just say a few introductory words.
The gender can either refer to a social role based on the sex of the person (gender role) or personal identification of one's own gender based on personal appreciation (gender identity). The two most common genders are male and female which are named after their sexual equivalent. However, there are other types of genders. Btw, you might want to make sure to avoid confusion between gender and sexual orientation. It is also important to distinguish between "gender role and "gender identity"
Have a look at wikipedia > Sex and gender distinction for more information.
Note that, in biology, as we are not dealing with the social construct of the gender, we tend sometimes to use the term 'gender' as a synonym of 'sex'. Using the term gender instead of sex also has the advantage in biology to avoid the confusion between 'sex', 'sexual reproduction' and 'sexual organ'. I will below use the term 'sex' and 'gender' as defined by sociologists.
Answering in the text
These days it is often contested how many genders is there. So my question is how many genders is there[?]
There is no true answer to this question. There are as many genders as we want to as it is a social construct. There are only two sexes (and limit cases).
is it unnatural for evolution to generate multiple genders.
For reasons explained above, the question makes no sense. But let's replace 'gender' by 'sex' and rephrase your question as
is it unnatural for evolution to generate multiple sex?
There are species with a number of genders different from two. There are of course also species where single individuals have carry organs of both sexes. There are species where reproduction is asexual. There are species with sex but very little sexual dimorpisms (thanks @TimonG.), there are species with sexual reproduction but not sexes (sometimes mating types), etc... So, no it exists.
In humans however, there are only two sexes (plus limit cases).
Sex and sexual orientation
Of course, sex and sexual orientation are not the same thing. While there are only 2 sexes in humans (and as many genders as we want), there may be a lot of different sexual preferences. In fact, if we go into the details there are probably as many sexual preferences as there are people! Typically, we categorize those sexual preferences into a few sexual orientation. Note that there is nothing "unnatural" (whatever this term mean) to having a sexual orientation that differ from what the majority of the people with the same sex have.
You might want to read the post How can homosexuality evolve despite natural selection?