grammar vs the grammar

I'm now fighting with the noun "grammar" since I am not able to comprehend whether I've got to use "the" with that abstract noun, or not, or it's even optional.
Maybe when I'm talking about some specific language's grammar, I have to use "the"?for example:
• I've always hated grammar since it tells me what to do(in general)
• According to [the] grammar, you can certainly say "vulgarer"(referring to specifically [the] English grammar)
• [The] Russian grammar is even more complex than the German one.
Could you help me figure out the hardest question in the solar system?🏵🌻
  • The is a determiner - basically a demonstrative adjective - the <noun> means "that exact/particular noun of which we (speaker and listener) are [now] aware.”

    (The is similar to “that” - in fact it is a form of the Old English “that” and often “that” can be used in place of the.)

    The is used

    (i) where the noun refers to something specific that is well known to everyone:

    "The moon is bright" "The Kremlin is in Moscow" "The weather is bad." (Everyone is aware of the the moon and the Kremlin and weather.)

    This applies also to the use of “the” to identify a class of nouns that the listener is expected to know or where any of the following categories applies: "The dog (= any creature known as "a dog") makes a good pet." "The harp (= any musical instrument known as "a harp") is difficult to learn." "The oak lives for 600 years (= any tree known as "an oak"); “The car was an incredibly good invention.” (= any mode of transport known as "a car.")

    (ii) where the noun has been already mentioned so that the speaker and listener are aware of the exact thing that is being discussed:

    "I saw a *(= a random example of a)* cat in my garden this morning. The cat *(speaker and listener now know exactly which cat is being discussed)* caught a *(= a random example of a)* bird but the *(speaker and listener now know exactly which bird is being discussed)* bird escaped."

    (iii) where the noun is defined or described so that the listener will know what sort of 'noun' it is:

    "I saw the man that I met in Paris." that I met in Paris defines "man" and the listener now knows exactly which man you are talking about.

    "The decision to shoot the prisoners was made." to shoot the prisoners" defines "decision" and the listener now knows exactly which decision you are talking about.

    (iv) where the noun is later/retrospectively defined or described so that the listener realises which particular noun was being referred to:

    "The cat stretched its legs and slowly walked across the room. It had lived in a small box below the window since John had rescued from the river”: lived in a small box below the window since John had rescued from the river makes the listener/reader aware of exactly which cat this is. You therefore use “the”.

    (iv) to modify an uncountable noun by confirming the identity of that noun:

    “I have information that you need” – no article -> “I have [some / an example of / examples of] information of which you are unaware but which you need.”

    “I have the information that you need” – article -> “I have that information that both you and I are aware that you need.” (You and I are aware because either (i) you have asked us for it, or (ii) I mentioned earlier.)#

    In both of these examples, you will see that “that you need” defines “information”, so you might think that “the” could be used in both. But it cannot be used in the first because only I am aware of the information – and in order to be able to use “the” we must both be aware.

    In your case:

    I can teach you grammar = I can teach you anything that can be described as "grammar".

    I can teach you the grammar that you need.