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

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 !