In Jain Dharma, Simandhar Swami is definitely accepted as real (satya / truth) within the Jain cosmological framework.

Who is Simandhar Swami?

• He is a living Tirthankar (Arihant).
• He resides in Mahavideh Kshetra, a special pure region in the Jain universe.
• There, Tirthankars are always present and continuously give divya deshna (divine discourses) for the liberation of souls.

Is this “true” in Jainism?

• According to both Digambar and Shwetambar scriptures, Mahavideh Kshetra exists and living Tirthankars are present there right now.
• Simandhar Swami is one of those presently living Tirthankars.
• We in Bharat Kshetra (our world) are in a time-cycle (5th ara) where no new Tirthankars take birth, so we cannot meet Him physically, but His existence is accepted as tattva (truth) in Jain cosmology.

Tradition-wise understanding (short):

• Shwetambar:

- Very open, direct devotion to Shri Simandhar Swami. - Many temples, stavans, and daily prayers remember Him, with the bhav (feeling) to get rebirth in Mahavideh Kshetra and attain moksha there.

• Digambar:

- Fully accepts living Tirthankars in Mahavideh Kshetra as a principle. - Personal, name-specific devotion to Simandhar Swami is usually less emphasized in practice, but the doctrine is consistent.

Spiritual meaning for us:

• Remembering a living Tirthankar strengthens:

- Samyak Darshan (right faith) - Samyak Jnan (right knowledge) - Samyak Charitra (right conduct)

• By ahimsa, aparigraha, and good sadhana here, we create the causes to be reborn in Mahavideh Kshetra, listen to Simandhar Swami’s discourses, and attain moksha.

You can read a simple explanation here