Using present participle as an adverb: "having a coffee and catching up" is used here as a present participle to describe the activities of people in cafes, making the sentence more vivid and specific.
Past participle as an adjective: "popped up" as a past participle, used to modify "cafes", indicating the widespread distribution of cafes, adding descriptive and complexity to the sentence.
Infinitive as purpose adverb: "to relax" and "to do this" are used as infinitives to express purpose, explaining the reasons for people engaging in social activities, enhancing the logicality and clarity of the sentence.
Passive voice: "are maintained and strengthened" using the passive voice to describe the results of friendship, demonstrating the diversity of language and the accuracy of expression.