Can a Lead Auditor certify that organisation is ISO 27001 compliant?

Only auditors working for certification bodies (certification auditors) can certify a business as ISO 27001 compliant.

The choice of the certification body is an organization's decision, based on its strategies and business objectives and alignment with certification body practices.

These articles can provide you further information:

• How to choose a certification body https://advisera.com/blog/2021/01/11/how-to-choose-an-iso-certification-body/
• Becoming ISO 27001 certified – How to prepare for certification audit https://advisera.com/27001academy/iso-27001-certification/