Since Japan's commercial whaling resumed in July 2019, some people, mainly those who are involved in whaling, have seemed to have cheered up.

I think that 99.9 percent of Japanese people hate to eating whales.

It appears that about 600 whales had been caught aeach year undefor research purposes before Japan's commercial whaling resumption.

Despite it being for "research purposes", whales caught in the Antarctic waters ended up as sashimi or steak on plates.

Ironically, under the commercial whaling, the annual quota may go down according to the article.

Since Japan's commercial whaling resumed in July 2019, some people, mainly those who are involved in whaling, have seemed to have cheered up.

Could also say "they seem to have become excited"

I, personally, do not want to admit to the fact that Japan has been conductingactively huntsing.

I think that 99.9 percent of Japanese people hate to eating whales.

"I hate (noun)" and in English the noun form of the verb is identical to the gerund.

It appears that about 600 whales hadve been caught a/each year undefor "research purposes" before Japan's commercial whaling resumption.

The last part of this sentence is grammatically correct but sounds a little stuffy. "... Before Japan resumed (commercial) whaling".

Despite itwhales being caught/captured for "research purposes", whales caught in the Antarctic watersmost of them actually ended up as sashimi or steak on plates.

You should state what "it" is, because there's lots of stuff going on in this article. Instead of "most of them" you can also say "they".

Ironically, under the commercial whaling policies, the annual quota may go down according to the article.

I read an article about a whale restaurant in Tokyo today.

I think it sounds more natural to add 'today' here because otherwise you could have read this article a few years ago. While it is implied through the title of the post I think it would look more natural like this.

Since Japan's commercial whaling resumed in July 2019, some people, mainly those who are involved in whaling, have seemed to have cheered up.

Using 'have seemed' implies that they have finished seeming cheered up while I think they still seem to have cheered up from this development.

It appears that about 600 whales had been caught aper year undefor research purposes before Japan's resumed the commercial whaling resumption.

Something can be done 'for' a certain purpose, here you could also maybe use 'under the pretence of' since it turned out to be somewhat of a lie.

Despite it being for "research purposes", whales caught in the Antarctic waters ended up as sashimi or steak on plates.