Se secó hasta el punto de que se rompió.

Here secarse means to dry up / to become dry.

So se secó does not usually mean it dried itself in a literal reflexive sense. Instead, this se is part of the verb as it is often used in Spanish to describe a change of state:

• secar = to dry something
  
  • El sol secó la ropa. = The sun dried the clothes.
• secarse = to become dry / to dry out
  
  • La madera se secó. = The wood dried out.

In this sentence, the idea is that something became so dry that it broke.

Secó is the preterite form of secarse.

The preterite is used because the sentence describes a completed event in the past:

• it dried out
• and then it broke

So se secó means it dried out or it became dry as a finished action.

For a similar reason. Romper means to break something, while romperse often means to break / to become broken.

• Juan rompió el vaso. = Juan broke the glass.
• El vaso se rompió. = The glass broke.

In your sentence, se rompió means that the thing ended up broken, without focusing on who caused it. The cause is understood from the context: it got so dry that it broke.

Not necessarily. In English, it broke itself sounds very literal and unusual. In Spanish, se rompió is very commonly used simply to mean:

• it broke
• it got broken
• it ended up broken

So it is usually better to understand se rompió here as it broke, not as a literal reflexive action.

Hasta el punto de que means to the point that or to such an extent that.

It introduces the result of the first action:

• Se secó = it dried out
• hasta el punto de que se rompió = to the point that it broke

So the whole structure shows degree + consequence.

A very close English pattern is:

• It dried out to the point that it broke.

Because hasta el punto de que is the normal fixed expression.

Think of it as built around the noun punto:

• el punto de que...

So after punto, Spanish uses de before the clause.

Standard Spanish is:

• hasta el punto de que...

Not normally:

• hasta el punto que...

Yes. That is a very natural alternative.

• Se secó hasta el punto de que se rompió.
• Se secó tanto que se rompió.

Both mean roughly the same thing.

The difference is mainly style:

• hasta el punto de que sounds a bit more explicit or formal
• tanto que sounds more everyday and direct

The subject is not stated explicitly. Spanish often omits the subject when it is clear from context.

So se secó and se rompió could refer to:

• la madera = the wood
• la piel = the skin
• el plástico = the plastic
• una rama = a branch
• etc.

The sentence by itself just means it dried out to the point that it broke, and the listener is expected to know what it refers to from the previous context.

No, not in the usual sense.

Even though English learners sometimes see se and think of a passive, here this is better understood as a pronominal/intransitive use showing a change of state:

• se secó = became dry
• se rompió = broke / became broken

A true passive would be something like:

• Fue roto = it was broken

But that is not what this sentence is doing.

Because the result is being presented as a real, completed fact.

• se rompió is indicative because it actually happened

In this sentence, the speaker is not talking about a hypothetical or uncertain result. They are saying that the drying really reached that point, and the object really broke.

Yes, but that is a different use.

• Secarse can mean to dry oneself
  • Me seco con la toalla. = I dry myself with the towel.

But it can also mean to dry up / become dry

• La planta se secó. = The plant dried up.

In your sentence, it is clearly the second meaning: to become dry / dry out.

A couple of things, if you are learning Spanish from Spain:

• secó: the c before o is a normal k sound
• h in hasta is silent
• z or c before e/i would often sound like th in much of Spain, but this sentence does not contain that exact case in a key way except in forms you might compare, like secarse with c + a/o still being k
• rompió has stress on the final syllable: rom-pió

So a rough pronunciation would be:

• seh seh-KOH AS-tah el PUN-toh deh keh seh rom-PYOH

The overall idea is:

• something became so dry that it broke

A very natural interpretation is:

• It dried out so much that it broke.
• It got so dry that it cracked/broke.

Depending on context, broke might also be translated more naturally as cracked, especially for things like skin, wood, earth, or plastic.