DS-9632NI-ST is a discontinued model, quite an old one. DS-9632NI-I8 is a current generation model.
Some differences just to name a few, but there are many more.
NI-ST - up to 5MP, 160Mbps bandwidth, H264, 4 SATA ports, normal HDMI
NI-I8 - up to 12MP, 320Mbps bandwidth, H265, 8 SATA ports, 4K HDMI