So when "apparently" modifies the whole sentence or clause that follows it then it should be followed by a comma. Correct: Apparently, he doesn't have a clue.

Can we start a sentence with apparently?

Apparently is an adverb that is often used at the beginning of a sentence. When this happens, follow the above rule and use a comma. Example 1: Correct: Apparently, he was hungry!

Do you need a comma after an adverb at the beginning of a sentence?

Use commas after introductory words

It's common to use adverbs to start a sentence. Always add a comma after adverbs that end in “ly.” Other introductory words or phrases that require a comma after them include “however,” “on the other hand,” and “furthermore.”