Can shareholders of listed companies buy shares in subsidiaries (non-holding companies) of listed companies?

Yes, you can. Whether the subsidiary is controlled by a listed company.

However, special attention should be paid to related party transactions and horizontal competition. If there is no related party transaction and no horizontal competition, there will be no big problem.

Of course, the CSRC is more concerned about why listed companies do not hold shares but only participate in this subsidiary! If there are related transactions, it will be very troublesome. It is inevitable to have doubts about the transfer of benefits.