Many scriptures Including puranas portrayincluding Puranas portray Lord Ganesha as Supreme Brahman.
Here in Ganesh Purana - Chapter 10 - Vyasa’sVyasa's Questions - Lord Brahma tells Shee Ved Vyasa that Shree Ganesha is supreme Brahman.
अजं निर्विकल्पं निराकारमॆकं निरानन्दमानंदमद्वैतपूर्णम् ।
परं निर्गुणंपरं निर्गुणं निर्विशेषं निरीहं परब्रह्मरूपं गणेशं भजेम् ॥1॥
Ajam nirvikalpam niraakaaramekam
Niraanandam Niraanandam aanandam advaita poornam poornam
Param Param nirgunam nirvishesham nireeham
Para brahma roopam roopam Ganesham bhajema
Brahmā Viṣṇu and Maheśa spoke: We should worship Gaṇeśa, Who is unborn, Who is free from change, Who is beyond taking forms (or actions), Who is unique, Who is without a support, Who is without a second, Who is bliss, Who is complete, Who is supreme, Who is beyond qualities, Who is absolute, Who is without passion, Who is supreme, and Who is Brahman. -
Also our famous Ganapati Atharvashirsha (Ganapati Upanishad) says so.
त्वमेव प्रत्यक्षं तत्त्वमसि ।
त्वमेव त्वमेव केवलं कर्ताऽसि ।
त्वमेव केवलंत्वमेव केवलं धर्ताऽसि ।
त्वमेव त्वमेव केवलं हर्ताऽसि ।
त्वमेव सर्वं खल्विदं ब्रह्मासि ।
त्वं त्वं साक्षादात्माऽसि नित्यम् ॥2॥
Tvam-Eva Pratyakssam Tattvam-Asi |
Tvam Tvam-Eva Kevalam Kartaa-[A]si | |
Tvam Tvam-Eva Kevalam Dhartaa-[A]si |
Tvam Tvam-Eva Kevalam Hartaa Hartaa-[A]si |
Tvam-Eva Sarvam Khalv[u]-Idam Brahma-Asi |
Tvam Tvam Saakssaad-Aatmaa-[A]si Nityam ||2||
(O Ganapati) You indeed are the visible Tattvam (Conscious Essence underlying everything), (O Ganapati) You indeed are the only Creator (Karta) (by Whose Power the Universe is Created), (O Ganapati) You indeed are the only Sustainer (Dharta) (by Whose Power the Universe is Sustained), (O Ganapati) You indeed are the only Destroyer (Harta) (by Whose Power the Universe is finally Dissolved in its Conscious Essence), (O Ganapati) You indeed are All This (The Universe); You verily are the Brahman (giving Consciousness to All), (O Ganapati) You are the visible Atman, the Eternal (underlying Reality).