I'm still a newbie, but from what I've read, は is usually used when a sentence is negative. が tends to add some importance or emphasis to whatever word it follows, so the meat would be the most important part of the sentence if you used が. With は, the emphasis is shifted to the "not liking" which makes more sense.

"Do you like meat?" "にくが好きですか" "I don't like meat." "にくは好きじゃないです"

The "not liking" is the important new information in the sentence, so the meat just gets a は, marking it as already-known information. This shift in emphasis happens a lot when you turn something negative.

Commonly yes but it's only a short sentence so は still works as a subject marker.

I noticed that "は" is used in negative sentences, like in the "日本語は話せません (日本語 は はなせません)" X "日本語が話せます (日本語 が はなせます)" : I don't speak Japanese X I speak Japanese. I hope that this is not a mistake of Duolingo. (^ v ^)

When we want to highlight what we like, we can use は before 好き。

I thought きらい meant a more stronger feel of dislike, mainly "to hate"

Do not like 好きではない(です) or 好きではありません

'好きじゃない' is more casual than '好きではない'.

It is used when conversation.

きらい is too strong of a word and not particularly used in conversations. It's not wrong to use it but if you do people may not like you

nikuwa sukijanaides

好きis an adjective. So you use じゃない which is the negative form of です

Because it's an adjective in Japanese rather than a verb like in English

Do you mean じゃない？It's just a more colloquial form of "ではありません". In speech "では" tends to get pronounced as "じゃ" so can be written that way too.