a group of people (is/are) ...

In American English, collective nouns like "group," "team," "squad," etc. are treated like regular nouns. In other words, since "a group" is singular, it would require "is" (not "are").
In British English, collective nouns are more often treated as plurals that require plural verbs. Therefore, it would be "a group of people ARE ..."
Since we admins are Americans, we would say "A group of people IS waiting patiently in line." However, our friends in other parts of the world are more likely to say "A group of people ARE waiting patiently in line."
We hope this helps! 👍🏻