1980s or 1980’s is a tricky one.
.....................................
1980s is a period during which we had great musicians.........
Subject, noun
1980’s haircuts were very different......
The apostrophe denotes possession....The haircuts were owned by the 1980s.
Technically 1980’s would refer only to possesive of the year 1980. The decade 1980s possesive would be 1980s’. The only appropriate use of the apostrophe is in the truncation as in ‘80s.