Форматирование то и дело меняется.

Because форматирование is the subject of the sentence: it is the thing that changes.

• форматирование = formatting
• меняется = changes / is changing

So форматирование stays in the nominative singular.

If you changed the sentence so that formatting was the object, the case would change. But in Форматирование то и дело меняется, it is the thing doing the changing, so nominative is exactly what you expect.

То и дело is a fixed idiomatic expression. It does not mean something like that and business if translated word-for-word. As a whole, it means:

• constantly
• again and again
• every now and then
• keeps ...-ing

The exact English translation depends on context.

In this sentence, it suggests repeated change, often in a slightly annoying or noticeable way:

• Форматирование то и дело меняется.
• The formatting keeps changing.

So it is best learned as a chunk: то и дело.

Russian word order is flexible, and adverbial expressions like то и дело can often move around.

Here, the structure is:

• Форматирование — subject
• то и дело — adverbial expression
• меняется — verb

This placement is very natural. It puts the repeated nature of the action right before the verb.

You could also hear:

• Форматирование меняется то и дело.

That is also understandable, but Форматирование то и дело меняется sounds especially smooth and natural.

Because the sentence means changes in the sense of changes by itself / is undergoing change, not changes something else.

Compare:

• менять = to change something
• меняться = to change, to be changing

So:

• Он меняет настройки. = He changes the settings.
• Настройки меняются. = The settings change / are changing.

In your sentence:

• Форматирование меняется = The formatting changes / is changing

The -ся matters because the subject is not actively changing another object; it is itself the thing undergoing change.

Grammatically, меняется is present tense: changes / is changing.

But because of то и дело, the whole sentence gets the meaning of repeated action:

• changes again and again
• keeps changing

So the repetition is not built into the verb form itself; it comes from то и дело.

Because форматирование is a singular neuter noun.

Russian verbs in the present tense agree with the subject in person and number. Here the subject is:

• форматирование — singular

So the verb is also singular:

• меняется — 3rd person singular

If the subject were plural, the verb would be plural too:

• Настройки то и дело меняются.
• The settings keep changing.

Форматирование is neuter.

A very common clue is the ending:

• nouns ending in -ие are often neuter
• форматирование ends in -ие

Because it is neuter singular, in the present tense the verb still uses the normal 3rd person singular form:

• форматирование меняется

You do not see gender directly on the present-tense verb, but gender becomes important in the past tense:

• Форматирование менялось. = The formatting was changing / kept changing.

The past-tense ending -лось shows neuter.

Yes. Постоянно is possible and natural.

But there is a nuance:

• постоянно = constantly, continuously
• то и дело = repeatedly, over and over, every so often

So:

• Форматирование постоянно меняется sounds more neutral and continuous.
• Форматирование то и дело меняется often suggests recurring changes that keep happening and may be a bit bothersome or noticeable.

In many contexts they are close, but they are not perfectly identical.

Grammatically, форматирование is the noun formatting. It usually refers to the process or state of formatting.

In real usage, though, Russian sometimes uses abstract nouns in places where English might prefer something more concrete, like:

• the formatting
• the layout
• the text formatting

So in context, форматирование may refer to the formatting setup or appearance that keeps changing.

If you wanted to be more specific, you might also see things like:

• формат текста = text format
• оформление = design / presentation / layout
• разметка = markup / layout structure, depending on context

But your sentence as written is perfectly normal.

It can be used with many verbs, especially when you want to show that something happens repeatedly.

For example:

• Он то и дело звонит. = He keeps calling.
• Она то и дело смеётся. = She keeps laughing.
• Компьютер то и дело зависает. = The computer keeps freezing.

It is especially common when the repeated action is noticeable, frequent, or slightly irritating.

So yes, it is broadly usable, but it works best with actions or events that recur.

Usually no. Форматирование меняется normally means the formatting changes / is changing / keeps changing, not someone is changing the formatting.

Russian -ся verbs can sometimes overlap with meanings that English expresses differently, but here меняется is best understood as an intransitive/reflexive-style verb meaning undergoes change.

If you wanted a clearer passive idea like is being changed, Russian would usually express it differently, for example with context or another construction. In this sentence, the focus is simply that the formatting does not stay stable.

The stress is:

• формати́рование
• то и де́ло
• меня́ется

So the whole sentence is pronounced roughly like:

• формати́рование то и де́ло меня́ется

Stress is worth learning early because Russian spelling does not show it in normal writing, and wrong stress can make a familiar word harder to recognize.