In Jain temples, the main pratima (Mulnayak) is normally a Tirthankar, not a siddha. Siddhas (liberated souls) are not worshiped as the primary idol of a temple. They may be present as additional pratimajis in some places, but the Mulnayak is typically a Tirthankar.

• Taranga Jain Temple is described as a siddha kshetra, but its Mulnayak is Adinath (not a siddha). ( jainknowledge.com)
• Siddhachalam’s main temple has Mulnayak Bhagwan Adinath and other tirthankaras; siddha idols exist in other parts/temples there, but not as the sole main pratima. ( siddhachalam.org)

You can read more about these temples here and here and .