Mi hermana prefiere el yogur con mango, pero yo quiero probar el coco con miel.

Because the verb is preferir, and in the present tense it is a stem-changing verb: e → ie in most forms.

With mi hermana, the subject is she, so you need the él/ella/usted form:

• yo prefiero
• tú prefieres
• él/ella prefiere
• nosotros preferimos
• vosotros preferís
• ellos prefieren

So Mi hermana prefiere means My sister prefers.

After querer when you mean to want to do something, the next verb stays in the infinitive.

So:

• quiero probar = I want to try
• quieres comer = you want to eat
• queremos ir = we want to go

So quiero pruebo would be incorrect, because you do not normally conjugate both verbs in this structure.

That is true: Spanish often drops subject pronouns because the verb ending already tells you who is doing the action.

So you could say:

• ...pero quiero probar...

However, yo is included here for contrast and emphasis:

• My sister prefers X, but I want to try Y

So pero yo quiero... sounds a bit like but I want..., with extra stress on the difference between the sister and the speaker.

Spanish uses definite articles more often than English, especially when talking about a specific item, option, or type.

Here, el yogur con mango is not just yogurt in general. It means something like:

• the mango yogurt
• the yogurt with mango
• that yogurt option with mango

Likewise, el coco con miel points to a specific option or choice in context.

Yes, in standard Spanish it is usually masculine:

• el yogur

In Spain, yogur is a very common spelling. You may also see yogurt, but yogur is perfectly normal and very common.

Its plural is usually:

• los yogures

Con means with, so it suggests the food comes with that ingredient.

• yogur con mango = yogurt with mango
• coco con miel = coconut with honey

By contrast, de often suggests flavour, type, or made of:

• yogur de coco = coconut yogurt
• helado de vainilla = vanilla ice cream

So the difference is often:

• con = with an added ingredient or accompaniment
• de = of that flavour/type

In real life, context matters, and sometimes the line is not completely rigid, but that is the main idea.

In a food context, probar usually means to try or to taste.

So here:

• quiero probar el coco con miel = I want to try/taste the coconut with honey

This is different from intentar, which means to try in the sense of to attempt.

For example:

• Quiero probar el yogur = I want to taste the yogurt
• Quiero intentar hacerlo = I want to try to do it

Literally, yes, el coco con miel means the coconut with honey.

But in context, Spanish can use the ingredient or flavour name as a shorthand for an option, especially if people are choosing between foods or desserts.

So it may be understood as something like:

• the coconut one with honey

If you wanted to make the parallel with el yogur con mango more explicit, you could say something like:

• el yogur de coco con miel
• el de coco con miel

The original sentence relies on context to make the meaning clear.

You can, but it changes the feel slightly.

• prefiere yogur con mango sounds more general
• prefiere el yogur con mango sounds more like a particular option, type, or item

So the version with el feels more specific and natural if the speaker is choosing among particular yogurts or flavours.

Pero means but.

It connects two contrasting ideas:

• Mi hermana prefiere...
• pero yo quiero probar...

So the sentence sets up a contrast between the sister’s preference and the speaker’s preference.

Mi hermana is the normal, simple way to say my sister.

Spanish has two main possessive patterns:

• mi hermana = my sister
• la hermana mía = the sister of mine

The first one is much more common in everyday speech. The second is possible, but it is usually more emphatic, stylistic, or used in special contexts.

Also, notice that mi does not change for masculine or feminine singular:

• mi hermana
• mi hermano

Only the plural changes:

• mis hermanas
• mis hermanos

Yes, it is natural.

A very normal structure is:

• [statement], pero yo + verb...

That works well here because yo adds contrast.

You could also say:

• Mi hermana prefiere el yogur con mango, pero quiero probar el coco con miel.

That is also correct, but it has a little less emphasis on I.