I have over 20000 parts i need to change to rigid bodies, how do i do that all at once?

Setup Rigid Body on one object first, then select all other objects you need it applied to (not the one you set), then make sure the very last object you select is the one you set the Rigid Body on. This is called the Active Object.

You will know you've done it correctly as all objects except the Active Object will have dark orange outlines and the Active Object will be the standard orange outline color.

To then apply the same Rigid Body settings to all those objects, in Object Mode, go to Object>Rigid Body>Copy from Active.

If you select everything. The object tab in the top left part of the screen has a rigidbody section where it adds it to all selected obejcts

This will probably crash your computer so be careful.