Noch maandag noch dinsdag is beschikbaar als opvangdag.

Noch ... noch is the Dutch equivalent of neither ... nor.

So:

• noch maandag noch dinsdag = neither Monday nor Tuesday

It links two alternatives and says that neither of them fits the statement that follows.

This structure is a bit more formal or written than some other Dutch ways of saying the same thing.

In Dutch, days of the week are normally written with a lowercase letter, unless they start a sentence.

So Dutch writes:

• maandag
• dinsdag
• woensdag

This is different from English, where Monday and Tuesday are capitalized.

The sentence treats the two days as separate single options: neither Monday nor Tuesday is available.

Because the linked items are singular, Dutch commonly uses singular is here.

So the structure is understood as:

• Monday is not available
• Tuesday is not available

rather than as one plural group.

It is correct Dutch, but it sounds somewhat formal or written.

In everyday speech, people often use simpler alternatives, such as:

• Maandag en dinsdag zijn allebei niet beschikbaar als opvangdag.
• Zowel maandag als dinsdag zijn niet beschikbaar als opvangdag.
• Geen van beide dagen is beschikbaar als opvangdag.

So the original sentence is fine, but not the most conversational option.

Because beschikbaar comes after is and functions as an adjective used predicatively.

In Dutch:

• before a noun, adjectives often get an ending:
  een beschikbare dag
• after zijn, they usually do not:
  de dag is beschikbaar

In your sentence, beschikbaar comes after is, so it stays in its basic form.

Als here means as in the sense of in the role of or for use as.

So beschikbaar als opvangdag means:

• available as a childcare day
• available to serve as a daycare day

This tells you in what capacity the day would be available.

Opvangdag is a compound noun:

• opvang = childcare / care / day care
• dag = day

Dutch forms compound nouns very freely, so combining words like this is very normal.

Depending on context, opvangdag can mean something like:

• a childcare day
• a daycare day
• a day on which childcare is provided

In Dutch, days of the week are usually used without an article when you mean the day in a general naming sense.

So:

• maandag
• dinsdag

not normally:

• de maandag
• de dinsdag

You can use an article in some special contexts, but here the simple bare form is the normal one.

After the subject, Dutch puts the finite verb in second position in a main clause. Here that verb is is.

Then the rest of the information follows:

• beschikbaar = the main description
• als opvangdag = extra information explaining in what role it is available

So the structure is:

• Noch maandag noch dinsdag = subject
• is = finite verb
• beschikbaar als opvangdag = predicate/complement

This is normal Dutch word order.

Yes. A native speaker might often choose a simpler sentence, for example:

• Maandag en dinsdag zijn niet beschikbaar als opvangdag.
• Geen van beide dagen is beschikbaar als opvangdag.
• Zowel maandag als dinsdag zijn niet beschikbaar als opvangdag.

These are often a bit more natural in conversation than noch ... noch, although the original sentence is still correct.

Not exactly.

• niet is the usual word for not
• noch is used in paired structures like noch ... noch

So you would say:

• Dinsdag is niet beschikbaar.
• Noch maandag noch dinsdag is beschikbaar.

You normally cannot just swap them freely. Noch has a special linking function, while niet is the standard negation word.