Telegram? WhatsApp?

ANSWER

TikTok. The Chinese-origin social media app for sharing short videos was the most downloaded app in 2021 and remained in first place during the first three months of this year, followed by Instagram. By app store, TikTok ranks first in the App Store, followed by YouTube; while on Google Play, the most downloaded app is Instagram, followed by Facebook. 

Here you can see the list of the top ten by downloads, according to VisualCapitalist.