Digambar Jainism has historically split into two broad major sub-sects, and from them some smaller ones formed over time. The two well-known “panthi” names you mentioned refer to how many founder-like leaders or lineages a group traced back to.

• 20-panthi (Bisapanthi): Also called Bisapantha. This is the older, more temple-worship–inclined branch that accepts a tradition of Dharma-gurus (Bhattarakas) and allows devotional rites in many temples. They tend to worship Tirthankaras with images and ritual offerings in many places. This is considered the "twenty" panthi because of its long, plural lineage and practice networks.

• 13-panthi (Terapanthi): This is a reform/contrast movement that began in the 17th century to limit Bhattaraka influence and to simplify worship, often emphasizing minimal idol worship and, in some places, not using flowers or other offerings. The name Terapantha literally means “thirteen panths,” referring to a historical grouping of thirteen founding authorities.

There is also a third major Digambara sub-sect called Taranapantha (Samaiyapantha), which focuses on venerating sacred books rather than idols, and a few smaller sub-sects like Gumanapantha and Totapantha that arose from further differences in practice. The overall picture is that the Digambaras split into multiple streams mainly over ritual practice, leadership (Bhattarakas vs. non-Bhattaraka), and views on idol worship.

If you’d like a concise overview in a single place, you can read more here