In the CPython reference interpreter, that VM can be found at

https://github.com/python/cpython/blob/main/Python/ceval.c

It's 3619 lines. It's explained in this 515 line file:

https://github.com/python/cpython/blob/main/InternalDocs/

For comparison, there is a pure Python bytecode interpreter, its VM is here:

https://github.com/nedbat/byterun/blob/master/byterun/pyvm2....

It's 1043 lines.