Is my wobbly crank arm missing something or it’s just a loose screw?

Nah that’s cooked – you’ll need a new non-drive side crankarm. You’ll need to:

– get the right length (165mm, 170mm, etc.) usually this will be stamped on it.
– Get the right square orientation. [Diamond vs. square](https://m.media-amazon.com/images/S/aplus-media-library-service-media/13f96df7-c119-47af-88e8-5f55651f2d71.__CR0,0,1940,1200_PT0_SX970_V1___.jpg).

The crank bolt needs to be torqued to ~40Nm. Which is a lot of torque. Don’t try and do it up with a piddly little allen key/wrench.

Get a new crank arm. Once they come loose, you can tighten them as much as you want but it WILL come loose again, typically worse

Crand AND bottom bracket to fix it right