Video from inside the Russian factory for Shahed-136 UAV

I don't believe this to be an underground facility, this would require massive pillars and support structures considering the large work spaces and ventilation and air regeneration systems in each workshop.

This is likely a compilation of footage from different industrial production sites (workers wearing different work uniforms in each workshop indicates different companies) assembled to appear like this is one gigantic drone factory for propaganda purposes.

Besides there is very little in automation, most is manual labour, there are no soldering robots, no assembly line or the like to optimize production output. Even the drones are manually moved between different production stages (03:19, 04:20). For a modern, war-critical factory (even the foundries at 03:58 appear very clean and newish), this is by no means impressive.

At 02:39, the whiteshirt propagand'orc interviews Timur Shagivaleev, director-general of the Alabuga special economic zone, a prominent site for Russian drone production that sources part of their workforce from Alubuga Polytechnic School students.

At 01:19-01:25, windows can be observed in the background, at 04:10 in the ceiling, both of which I would find an odd design detail for an evil overlord's underground drone lair?

(article with additional information by The Telegraph)