A vCenter that is managed by an SDDC manager in VCF will have various messages or banners indicating this.
The vSphere Client login screen will show:"vCenter Server Managed by SDDC Manager"
And once logged in, there will be a banner at the top of the vSphere Client showing: "This vCenter Server is managed by SDDC Manager. Making modifications directly in vCenter Server may break SDDC Manager workflows. Please consult the product documentation before making changes through the vSphere Client."
VMware Cloud Foundation
This is expected if vCenter was licensed for VCF or converted from VVF to VCF vCenter.
For vCenter instances that have transitioned from VCF to VVF licensing, please engage VMware Support by submitting a support ticket for additional assistance.