I know that some parts of the sentence can change but what I mean is: ihr is es, and I had seen that ich gehe es gut is wrong and the right is mir geht es gut, so in that situation is the same logic?
If yes, why in this case the es is in Dativ form but not in Nominativ form?
PS: Please, don't answer it as "One is right", describe it more to know why it is right, please.
First of all, "es" is the nominative form of the pronoun meaning "it". The dative form of "ihr" ("you", as in several people) would be "euch". "ihr" can also be the dative form of "sie" ("she"). I think you are confusing the two meanings of "ihr". Your examples are both grammatically correct, but they have different meaning:
"Ihr lernt deutsch." = "You learn German."
Here "ihr" is the second person plural pronoun meaning "you" (several people) and not the dative form of "sie" ("she").
"Sie lernt deutsch." = "She learns German."
In both of these cases, "ihr" and "sie" are in nominative case because they are the subject of the sentence, identifiable by the question "Who is learning German?".
Understanding how "I am fine" translates to "Mir geht es gut" (or just "Mir geht's gut") can be somewhat difficult. In English, the verb ("am") is conjugated based on the person being fine ("I"), but this is not the case in German.
In this context, the verb "gehen" is what is called an impersonal verb, meaning that it has a dummy subject after which the verb is conjugated. An example of an impersonal verb in English is
"It is snowing"
Here the pronoun "it" carries no real meaning, and "snowing" is therefore an impersonal verb.
We can see how this relates to our German sentence if we instead translate
"Mir geht es gut."
as
"It is going well for me."
We see that the subject of the sentence is actually "it". This means that "me" will receive either accusative or dative case since it is an object of the sentence. Deciding between accusative and dative can be rather difficult, and the most truthful answer is simply that you have to memorize that a lot of impersonal verbs take dative case, for example:
"Es gefällt mir." = "I like it."
"Es tut mir leid." = "I am sorry."
"Es schmeckt mir." = "It tastes well (to me)."
A clue that the case is dative might be that it is "for me" in the sentence since a rule of thumb is that objects which answer the question "For/to whom?" receive dative case.
Constructions with es like
Es geht mir gut.
are very special. Also gehen can be pretty confusing in its different kind of meanings and usage. So it's not a good idea to compare other phrases to that one.
If you mean (ihr is es) ihr is subject like es and therefor should be nominative, you're right. And actually it is nominative.
The ihr in
Ihr lernt deutsch.
is not dative (or genitive) of sie in
Sie lernt deutsch.
Instead ihr is second person plural pronoun here. Therefor you find both sentences and both are right but have different meanings.
