Comma after "Unfortunately" in the beginning of a sentence.

commas

Here, Cambridge doesn't use a comma. I am confused. Example in Cambridge Dictionary: Unfortunately we can't come this evening after all.

https://dictionary.cambridge.org/de/worterbuch/englisch/unfortunately

On different pages i found some rules telling there needs to be a comma. Examples follow:

We do usually put a comma after adverbs like 'unfortunately'. They are called 'sentence adverbs' because they modify the whole sentence and often give the opinion of the speaker/writer.

A parenthetical phrase adding detail to the main clause. Initially placed parentheticals are normally set off by a comma.

Cause I'm studying for my Level 2 graduation, i want going crazy reading here and there comma rules followed by looking in the Cambridge Dictionary without finding them there.

HELP me out please !

The Oxford Manual of Style has this to say about sentence adverbs:

Adverbs and adverbial phrases that comment on the whole sentence, such as therefore, perhaps, of course, are often enclosed in commas, but this is not a fixed rule. Sense may be altered by the comma's placement or presence. Consider the following:

We'll go to Cornwall, perhaps in the spring. (perhaps then)

We'll go to Cornwall perhaps, in the Spring. (perhaps elsewhere)

Again she refused to speak. (once more)

Again, she refused to speak. (in addition)

The ship's captain ordered a change, of course. (indeed?)

In your particular example, the use of a comma would appear to be optional (and therefore a matter of style), since it doesn't alter the meaning.