The Trimurti-s are only forms of One ‘Shakti’ – Kurmapuranam

In this chapter of the Ishwara Gita, the Lord Shiva says that the Trimurti-s involved in the three cosmic functions of creation, etc. are only manifestations of the One Shakti:
https://sa.wikisource.org/s/42i

अहं हि सर्वशक्तीनां प्रवर्त्तकनिवर्त्तकः ।
आधारभूतः सर्वासां निधानममृतस्य च ॥ ४.२०
I am the abode of the Shakti that is behind everything in creation.

एका सर्वान्तरा शक्तिः करोति विविधं जगत् ।
आस्थाय ब्रह्मणो रूपं मन्मयी मदधिष्ठिता ॥ ४.२१
One manifestation is the world-creating power that takes the form/name of Brahmaa.

अन्या च शक्तिर्विपुला संस्थापयति मे जगत् ।
भूत्वा नारायणोऽनन्तो जगन्नाथो जगन्मयः ॥ ४.२२
The other form of this Shakti takes the form/name ‘Narayana’ and sustains the world.

तृतीया महती शक्तिर्निहन्ति सकलं जगत् ।
तामसी मे समाख्याता कालाख्या रुद्ररूपिणी ॥ ४.२३

The third shakti manifestation is the power of destruction of the form/name Rudra.
The above is in tune with the Vishnu puranam discourse.https://adbhutam.wordpress.com/2018/11/15/vishnu-is-also-a-vibhuti-of-brahman-vishnupuranam/
https://adbhutam.wordpress.com/2018/11/12/turiya-shiva-and-vishnu/