When a dependent clause comes at the start of a complex sentence, you need to put a comma after it.

Question

When a dependent clause comes at the start of a complex sentence, you need to put a comma after it.

Answer 1

https://examples.yourdictionary.com/examples-of-dependent-clauses.html

at that link, you will find examples of dependent clauses at the beginning of the sentence.

Some of them have the comma and some do not.