>[1] Having grown up in North America where it is common to refer to mathematics as the singular "math", it is still weird to type "maths" even after having picked up the habit a few years ago.
Maths is also singular, it just ends with an S. (People who say "maths" say "maths is my favourite/worst subject", not "maths are")
Actually, many dictionaries specifically label "mathematics" as plural, but concede that the singular form is far more popular in practice.
I tend to find only one use case where I find a plural form simply appears more natural: prefixing it with "the", as in "The mathematics necessary to explain the universe are complex." Replacing the "are" with "is" just does not sound right. Funnily enough, the natural pattern with the North American "math" becomes "The math necessary to explain the universe is complex.".
Maths is also singular, it just ends with an S. (People who say "maths" say "maths is my favourite/worst subject", not "maths are")