Why am I majoring in humanities in this era?

Starting from this autumn, I will be an university student who majors in humanities.

(1) "An" is used before vowel SOUNDS, not vowel letters. A word can begin with a vowel letter but not a vowel sound, and the opposite is also true.
(2) "I" is singular, so "major" should be singular too ("majors").

Namely, hHumanities offer aare the science of humans.

"Namely" is not used this way; rather, it is used to introduce specific examples. Here's an example sentence: "Japan is widely known for its culture, namely anime." (Anime is a specific example of Japanese culture.)

Recently, humanities arhave often been criticized by man unspecified number ofy people.

(1) "Recently" refers to the past, so you should use "have often been" (past tense) instead of "are often" (present tense).
(2) "An unspecified number of people" is not a natural expression to use here. It makes it seem like you know the true number and are hiding it for some reason.

It is because humanities are not study of practical sciences.

I sympathize with thise opinion that students who majored in humanities cannot make a lot of money .

However I never endorse thise opinion that humanities are not worthy to studying.

I think "worth studying" sounds more natural.

Since AI have conspicus become ubiquitous, many actionvities which was used to be done by only human have not been human original activitys are no longer as such.

(1) "AI" is singular, so "have" should be too ("has").
(2) I question the use of "conspicuous" here. Allow me to suggest "ubiquitous" or "prevalent".
(3) "Actions" doesn't seem like the most appropriate word here. I'd suggest "activities".
(4) I reworded the second part of your sentence so that it sounds more natural.

I wouldon't say real work ishas been taken over by AI, but I'd say many human action, for example, get one'svities, such as getting ideas, checking, mak (what?), generating a sentences and communication, are shared with AI.

(1) I reworded your sentence so that it sounds more natural.
(2) It might be good to state what it is you're "checking".

Nevertheless consideration, our thoughts and real existence are not bothered by AI.

I think the pacing flows better with a comma behind "nevertheless".

When we are musing about our distinctiveown various questions, we can say we are doperforming human activityies.

The use of "distinctive" isn't very appropriate here.

Humanities are exist to make human bes human.

In the phrase "make humans human", "human" (the second one) is an adjective and not a noun.

WhenIf society deletecasts humanities, we are not even human aside, we will become humans no longer.

I rephrased your sentence so that it sounds more natural and fluent.

Why will I major in humanities in this era?

Starting from this autumn, I will be an university student who majoring in humanities.

Namely, humanities offer ateach the science of humans.

For example,: philosophy, literature, history and anthropology.

I sympathize thiswith the opinion that students who majored in humanities cannot make a lot of money .

However I never endorse thise opinion that humanities are not worthy tof studying.

Since AI havs become conspicuous, many actions which was used to be done by only human have not been human original activitypreviously could only be done by humans are now done by AI.

I dwon't say real work is taken over by AI, but I will say many human actions, for example, get one'sthinking of an idea, checking, and making a sentence and communication, are shareds, are done with AI.

Nevertheless considerationour ideas and real existence are not bothered by AI.

When we are musing about our distinctivunique questions, we can say we are doing human activity.

Humanities are exist to make humans be human.

When society deletes humanities, we are not even human.

Starting from this autumn, I will be an university student who majors in humanities.

Namely, humanities offer a science of human.

Recently, humanities are often criticized by an unspecified number of people.

Grammatically correct but "an unspecified number" is an odd thing to say. It's more normal to say "many people."

It is because humanities are not a (or the) study of practical science.

I sympathize with this opinion that a student (or students) who majored in humanities cannot make a lot of money .

Since AI havs become conspicuous, many actions which was used to be done by only humans have not been human original activitydone by computers.

I don't say real work is taken over by AI but I say many human action, for example, getting one's idea, checking, making a sentence and communication, are shared with AI.

Humanities are exist to make humans be human.

When society deletes humanities, we are not even human.