Bismillah.
The Takbeer is an aspect of the Sunnah of the Prophet [SAWS] that has been forgotten in recent times, so much so that we hardly see people making the takbeer. In fact, if you ask someone “Why aren’t you making takbeer during the first ten days of Dhul Hijjah?” they’d probably say “The first ten days are here already?!”
Watch this video to learn all about the Takbeer of Dhul Hijjah, in sha Allah: