In this sentence, amptelik means official.
Afrikaans often uses the same word form where English might distinguish between an adjective and an adverb. So amptelik can sometimes correspond to either official or officially, depending on the sentence.
Here, because it comes after is and describes die besluit, it is an adjective:
In another sentence, it could act more like officially.
Because after is, Afrikaans normally uses the basic form of the adjective.
So you say:
But when the adjective comes before the noun, it usually takes -e:
This is a very common pattern in Afrikaans:
Yes, in this sentence it is very close to English word order:
So it matches The decision is official quite neatly.
That said, Afrikaans often follows a verb-second pattern in main clauses. For example, if you move another element to the front, the verb still stays in the second position:
So this simple sentence looks very English-like, but wider Afrikaans word order has its own rules.
Afrikaans commonly uses a double nie in negative sentences:
That double negative structure is one of the most noticeable differences from English.