Is learning grammar important for a non-native speaker to master English?

It depends what you mean by learning grammar.
If you mean sitting and staring at a book full of grammar rules then I would agree that is not very helpful. It just leads to cognitive overload and prevents your from even making sentences.
But to produce language you do have to use grammar. Even if you just pushed two words out of your mouth, you'd still likely need to be careful about the order or change the form of at least one of them.
Natives don't learn a whole list of rules on how to do this. We do it by hearing lots of examples, working out the rule, and then trying to use it. In this way we acquire grammar, rather than by studying it.
When we get to school, by which time we have about 90% of the grammatical system worked out, we start getting told rules. At this advanced stage of grammar development these rules may be helpful to tweak a mostly working system. This is because we are not inhibited to speak and since we already have a high degree of fluency, we can use our monitor (as in Krashen's monitor hypothesis) to catch what we are saying and correct it before it leaves our mouth. But we are then only focused on a few rules... not every single grammatical rule. As I said before, that would be cognitive overload.
I have used the word rule here quite a bit, although I hate the word rule when it comes to grammar. Few rules are actually rules. They are better defined as tendencies. Almost any of them can be broken to achieve some effect.
So for non native speakers, this process of acquiring grammar is what I think is important. Exposure to the target language at the right level is important. A six year old native speaker has had about 16 hours a day x 365 days worth of exposure. That's almost 6000 hours.
However, native speakers acquiring grammar this way is not necessarily the fastest way. Who says we can't beat nature? Humans have been beating nature for thousands of years. So perhaps with exposure and the correct focused tasks we can help students to acquire grammar faster.
This brings us to inductive grammar teaching and ideas like guided discovery. This essentially means students see some input and then perform tasks designed to uncover the tendencies behind particular patterns. Of course this works best when the teacher has selected a text with good examples of the target structure and tasks that really do uncover that meaning. Designing these tasks is an art form.
Unfortunately both teachers and students everywhere are impatient and/or lazy. This process would appear to take longer than sitting and memorizing rules, so that is what people do. And amazingly when people don't get the results they want, they double down and do it twice as much.
So, yes, you do need to learn grammar to “master” English. However, you may not need to learn grammar in the way you think you need to.

🤔When should "In which", "at which", "from which" and "to which" be used?
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There is some confusion over when to use "in which," "at which," "from which" and "to which." The general rule is that the first three should be used to introduce a clause, while "to which" should be used to introduce a phrase.
However, there are exceptions to this rule.
For example, you might say "the book in which I found my pen" or "the store at which I bought my hat." In these cases, it sounds better to use the word that begins with a letter other than W.
@english_with_nab

I’ll post an audio book this week, it’s already done 😍… I’ve just sent it to our illustrator to make a beautiful design… 😇

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Do English speakers actually use the past perfect tense or past perfect continuous tense on daily conversations?

Yup, all the time, without thinking about it. When you grew up with the language it comes naturally.
The only thing in English that does not always come naturally is the conditional, which many people were never taught —or weren’t taught well—and didn’t hear used when they were growing up. Even for those who know it, it’s often dropped in casual conversation. (That is the conditional form, such as “If I were” instead of “if I was”). Also the subjunctive is fading from use.
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Little gift 😍

I guess years from now we will end up J do? 😂

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Did you ever = jeever