Het vasthouden van de ladder is vermoeiend.

No. Here het is not a dummy subject like English it in It is tiring.

In Het vasthouden van de ladder is vermoeiend, het is the definite article used with a nominalized infinitive. That means the verb vasthouden is being used as a noun-like expression:

• vasthouden = to hold / to keep holding
• het vasthouden = the holding / holding

So the whole subject is Het vasthouden van de ladder = holding the ladder.

Vasthouden is the infinitive of the separable verb vasthouden.

In this sentence, it is not acting like a normal finite verb. It is being used as a noun-like form after het:

• houden = to hold
• vasthouden = to hold on to / to keep holding

So het vasthouden van de ladder refers to the activity or act of holding the ladder.

Because vasthouden is a separable verb.

In the infinitive, it stays together:

• vasthouden
• ik wil de ladder vasthouden

But in a main clause with a conjugated verb, it usually splits:

• Ik houd de ladder vast.

So:

• het vasthouden van de ladder → infinitive, one word
• ik houd de ladder vast → finite verb, split apart

This is very common in Dutch separable verbs.

Because after a nominalized infinitive such as het vasthouden, Dutch often expresses the object with van.

So:

• het vasthouden van de ladder

literally looks like:

• the holding of the ladder

That is a normal Dutch way to build this kind of noun phrase.

If you use the infinitive more directly as a verb phrase, then you can keep the object without van:

• De ladder vasthouden is vermoeiend.

Both are possible, but the structure is different.

Yes. That is also grammatical and very natural.

Compare:

• Het vasthouden van de ladder is vermoeiend.
• De ladder vasthouden is vermoeiend.

The first sounds a bit more noun-like, because het vasthouden behaves like a noun phrase.

The second uses a bare infinitive phrase as the subject, which can feel a little more direct.

Dutch also very often uses another version:

• Het is vermoeiend om de ladder vast te houden.

That version is especially common in everyday speech.

Because this is not a te-infinitive construction.

Here vasthouden is part of a nominalized expression:

• het vasthouden van de ladder

In that structure, Dutch does not use te.

You do use te in a clause like:

• Het is vermoeiend om de ladder vast te houden.

So:

• het vasthouden → no te
• om ... vast te houden → yes te

Because vermoeiend is a predicate adjective here: it comes after is.

After zijn, Dutch adjectives normally do not take -e:

• Het werk is vermoeiend.
• De klim is zwaar.

But before a noun, they usually do take -e:

• een vermoeiende taak
• de zware klim

So in your sentence:

• is vermoeiend = correct

not:

• is vermoeiende

Because the whole subject, Het vasthouden van de ladder, is treated as one singular thing: one activity.

Even though the phrase contains several words, grammatically it is one singular subject, so Dutch uses:

• is

not:

• zijn

De ladder usually suggests a specific ladder, or a ladder already known from the context.

For example, if two people are painting a house and one person is holding a particular ladder, de ladder makes sense.

If you mean any ladder in a more general sense, you could also say:

• Het vasthouden van een ladder is vermoeiend.

So both are possible; the difference is the same basic one as in English:

• de ladder = the ladder
• een ladder = a ladder

No, it is grammatical and natural Dutch. But it is a slightly more noun-heavy way of saying it.

In everyday conversation, many speakers might prefer:

• Het is vermoeiend om de ladder vast te houden.

That said, Het vasthouden van de ladder is vermoeiend is perfectly normal, especially in written Dutch or when talking about an activity in a more abstract way.