"Your license for ESXi will expire in X days." as shown in the below screenshot.

VMware vSphere ESXi 8.x
This alert is seen if the license assigned to the ESXi host is an evaluation license or subscription based which is expiring in X days.
Assign a valid license to ESXi host. Refer to Managing licenses on ESXi hosts using the vSphere Client
Licensing and Subscription in vSphere
VMware End Of Availability of Perpetual Licensing and SaaS Services
Accessing VMware License folders and keys on the Broadcom support portal
Download license keys for Broadcom, CA, Symantec, and VMware products
Assign a License Key to an ESXi Host in the VMware Host Client