My usually chatty secondary school WhatsApp group was surprisingly silent, so I decided to try out the 'largatha trend. Is it grammatically correct? What does it mean and can it be rephrased?

Yes, your sentence is grammatically correct. The 'largatha trend' seems to refer to a specific trend that you might have observed on social media or in your peer group, but as of my last knowledge update, there isn’t any widely recognized trend by that name. It's possible it's something new or niche that has emerged recently. To clarify the sentence and possibly rephrase it while retaining the same meaning, you could say: "Noticing the usual chattiness of my secondary school WhatsApp group was surprisingly absent, I decided to try out the 'largatha trend.'" If you provide more context about what the 'largatha trend' entails, I can offer further suggestions or clarify its meaning.