Мякиш получился мягким.

Мякиш is the soft inside part of bread, as opposed to the crust. In English, this is often called the crumb of the bread.

So this sentence is probably talking about the result of baking or the texture of bread after cutting it open.

In this sentence, получиться means something like:

• to turn out
• to come out
• to end up being

So Мякиш получился мягким means that after baking or preparing it, the crumb turned out soft.

This verb is very common when talking about results:

• Торт получился вкусным. — The cake turned out tasty.
• Суп получился слишком солёным. — The soup turned out too salty.

It often suggests that the final result was discovered after the process.

Because after получиться in this meaning, Russian usually uses the instrumental case for the descriptive word.

So:

• мягкий = dictionary form, nominative
• мягким = instrumental masculine/neuter singular

This is similar to other verbs that describe becoming or being in some state:

• Он стал врачом. — He became a doctor.
• Хлеб получился вкусным. — The bread turned out tasty.
• Мякиш получился мягким. — The crumb turned out soft.

So мягким is not random: it is there because the verb structure calls for the instrumental.

Because it agrees with мякиш, which is a masculine singular noun.

Russian past tense verbs agree in gender and number:

• получился — masculine singular
• получилась — feminine singular
• получилось — neuter singular
• получились — plural

Compare:

• Хлеб получился вкусным. — masculine
• Булка получилась вкусной. — feminine
• Тесто получилось хорошим. — neuter
• Булочки получились мягкими. — plural

The -ся is the reflexive ending, but in many verbs it does not mean literal self-action like wash oneself. In получиться, it is simply part of the verb’s normal dictionary form.

Compare:

• получить — to receive, to obtain
• получиться — to turn out, to come out, to succeed

So here получился is not really something like received itself. It is just the standard verb used for a result.

It is an adjective.

More specifically, it is the adjective мягкий in the instrumental masculine singular form:

• nominative: мягкий
• instrumental: мягким

It describes the noun мякиш.

It is not an adverb.
If you wanted an adverb, you would use мягко, but that would describe how something is done, not what something is like.

Yes, but the meaning changes a little.

• Мякиш получился мягким. — The crumb turned out soft / came out soft.
  This focuses on the result of baking or preparation.

• Мякиш был мягким. — The crumb was soft.
  This simply describes it as a fact, without emphasizing the process or outcome.

So if you are talking about whether the bread came out well, получился is the more natural choice.

Usually not in the same context.

• стал мягким means became soft
• получился мягким means turned out soft

Стал мягким focuses on a change over time.
Получился мягким focuses on the final result of making something.

For example:

• Хлеб стал мягким — The bread became soft.
• Хлеб получился мягким — The bread turned out soft.

If you are evaluating the result of baking, получился is the better choice.

Yes. Russian word order is flexible, because the grammatical roles are shown by endings rather than position.

The neutral order here is:

• Мякиш получился мягким.

But you might also hear:

• Мягким получился мякиш.

That version puts more emphasis on мягким.

Even though the word order can change, the original version is the most straightforward and natural in most contexts.

Mostly, yes. Мякиш usually refers to the soft inner part of bread or a baked loaf.

In some contexts, it can be extended to mean the soft inside of something similar, but for a learner, it is safest to think of it mainly as the crumb of bread.

So this is a very food-specific sentence.

Получиться is perfective.

That matters because the sentence is about a completed result: after the baking or cooking was finished, the crumb turned out soft.

Perfective verbs often focus on:

• completion
• outcome
• one whole event

That fits this sentence perfectly.

A related imperfective form is получаться, which is used for repeated, habitual, or ongoing situations:

• У меня хлеб всегда получается мягким. — My bread always turns out soft.
• У меня хлеб не получается. — I can’t get the bread right / My bread doesn’t turn out well.

So получился here is the natural past-tense form for one completed result.

Yes, very common.

Russian often uses this pattern:

[thing] + получился/получилась/получилось/получились + [instrumental adjective/noun]

Examples:

• Пирог получился вкусным. — The pie turned out tasty.
• Кофе получился крепким. — The coffee turned out strong.
• Соус получился густым. — The sauce turned out thick.

So Мякиш получился мягким is a very typical and useful structure to learn.