Die Ankündigung nennt Samstag als Veranstaltungstag.

Nennt is the 3rd person singular present of nennen.

Here, nennen means something like:

• to name
• to state
• to mention
• to list as

So Die Ankündigung nennt Samstag als Veranstaltungstag means that the announcement identifies Saturday as the day of the event.

Useful forms of nennen:

• ich nenne
• du nennst
• er/sie/es nennt
• past: nannte
• past participle: genannt

Ankündigung is a feminine noun, so its dictionary form is die Ankündigung.

In this sentence, Die Ankündigung is the subject, which is why it appears in the nominative form:

• die Ankündigung = the announcement

So the structure begins with:

• Die Ankündigung = subject
• nennt = verb

Because this is a normal main clause in German, and German main clauses usually follow the V2 rule: the conjugated verb comes in the second position.

Here the sentence is:

• Die Ankündigung = position 1
• nennt = position 2
• Samstag als Veranstaltungstag = the rest

This is one of the most important word-order rules in German.

Because Samstag here is not being used as a time expression like on Saturday.

Compare:

• am Samstag = on Saturday
  This tells you when something happens.

• Samstag in this sentence = the day being named/identified
  This is part of the object of nennen.

So the sentence is not saying The event happens on Saturday in a simple adverbial way. It is saying that the announcement names Saturday as the event day.

Weekday names in German often appear without an article, especially when they are used simply as names of days.

So Samstag here is perfectly natural.

If you added an article, it would have to be den Samstag because Samstag is masculine and functions as the direct object here. But that would usually sound more specific or marked, as if you meant that particular Saturday.

So:

• Samstag = neutral, natural naming of the day
• den Samstag = possible in some contexts, but more specific/emphatic

Here als means as.

It introduces the role or label given to something:

• Samstag als Veranstaltungstag = Saturday as the event day

So als shows how Samstag is being classified.

This is different from other uses of als, such as:

• größer als = bigger than
• als ich jung war = when I was young

In this sentence, als is specifically the as meaning.

Samstag is functioning as the direct object of nennt, so it is in the accusative.

However, you do not see a special ending here because:

• Samstag is a noun used without an article
• the noun itself does not change form here

So even though it is accusative, it still looks like Samstag.

If you used an article, you would see the accusative more clearly:

• der Samstag = nominative
• den Samstag = accusative

Veranstaltungstag is a compound noun, which is very common in German.

It is made of:

• Veranstaltung = event
• Tag = day

So Veranstaltungstag literally means event day or day of the event.

In German, compound nouns are usually written as one word, and the last part determines the grammatical gender.

Since der Tag is masculine, der Veranstaltungstag is also masculine.

And like all nouns in German, it is capitalized:

• Veranstaltungstag

Sometimes German uses nennen without als, for example:

• Sie nannten ihn einen Helden.
  = They called him a hero.

So yes, German can use nennen + object + noun without als.

But in this sentence, als sounds very natural because it clearly marks a classification:

• Samstag als Veranstaltungstag

Without als, the sentence would sound awkward or at least much less natural here:

• Die Ankündigung nennt Samstag Veranstaltungstag.

That is not the best wording.

So in this sentence, keeping als is the normal choice.

Not completely. It is a mixed verb.

Important forms are:

• infinitive: nennen
• present: er nennt
• simple past: nannte
• past participle: genannt

So it has:

• a present-tense vowel change: nennen → nennt
• a past form that looks partly weak: nannte
• a participle with ge-: genannt

This is a verb worth memorizing because it is common.

It is natural, but it sounds somewhat formal and written, which fits the word Ankündigung.

You might also see similar formal sentences such as:

• Die Ankündigung gibt Samstag als Veranstaltungstag an.
• In der Ankündigung wird Samstag als Veranstaltungstag genannt.

In everyday speech, people might phrase it more simply depending on context. But as written German, the original sentence is perfectly normal.