We do, when we're distinguishing a population, say, on a cultural basis. For example, "Germans are industrious" or "Germans are known to be an industrious people."
I should add, I've heard it used usually when referring a tribe or old civilization like, "The Mayans were an advanced people for their time."
"Moderne" is an indeclinable adjective, meaning that it does not add a special ending for neuter or plural.
More specifically, "moderne" is in the group of adjectives ending in -e that do not decline. The group includes "lige" (equal) and "stille" (calm).
- en moderne bil = a modern car
- et moderne hus = a modern house
- moderne mennesker = modern people
Source: Danish: An Essential Grammar, by Tom Lundskaer-Nielsen and Philip Holmes, 2011 edition, paragraph 18.104.22.168., paper page 49, google book preview