In Jainism, every Arihant Bhagwan is _by definition_ “not yet Siddha”.

• Arihant = Kevali who has destroyed inner enemies (kashayas) and attained keval-jnan, but is still in a body.
• Siddha = Same soul after leaving the body and going to Siddha Shila (complete moksha).

So:

1. All 24 Tirthankar Bhagwans were at one time Arihant but not yet Siddha

Example: - Bhagwan Mahavir from the moment He attained keval-jnan (omniscience) till His nirvan was Arihant Mahavir, not yet Siddha. - After nirvan, the same soul became Siddha Mahavir.

1. At present in our Bharat Kshetra

- There is no living Arihant now. - Only Siddhas (liberated souls) exist at the top of the universe.

1. Example often given in Shvetambar tradition

- Shri Simandhar Swami in Mahavideh Kshetra is described as a present living Arihant (Tirthankar), so Arihant, not yet Siddha.

Summary: Any Tirthankar before nirvan = Arihant, not Siddha. After nirvan = Siddha.

You can read more about the meaning of Arihant here