Is not rolling a mint leaf on shabbos prohibed because of squeezing or extracting juice?
No juice is usually extracted when rolling a mint leaf. In addition, even if juice is extracted, one does not do anything with it, and there is no intention to squeeze out juice. It is therefore permitted to roll the leaf for purposes of extracting scent. However, one may not intentionally squeeze out liquid from the leaf.
There is no sechitah de’oraisa on leaves, but like fruit (other than grapes and olives, where there is a Torah prohibition) it is forbidden to intentionally extract liquid.