General steps are these:

1.       Put the ESXi host in maintenance mode - Compute
2.       Remove host from vDS switch - Compute
3.       Unmount and detach data LUNs / DO NOT DELETE DATA LUNS - Compute
4.       Remove host from the cluster (Remove from inventory) - Compute
5.       Delete boot LUN for the host, and remove host from the cluster – Storage
6.       Delete the service profile from UCS end - Compute
7.       Remove host from monitoring – SolarWinds
8.       Cleanup IPAM reservation, AD object and DNS reservation – Compute Windows
9.       Mark ESXi as decommissioned in CMDB – SNOW team

There might be some changes based on whether full cluster needs to be decommissioned.
In this case, the data luns can be deleted.

references:

How to properly decommission a VMware ESXi Host - The Tech Journal (stephenwagner.com)

Process in Short:
Enter Maintenance Mode
Remove Host from vDS Switches
Unmount and Detach iSCSI LUNs
Move host from cluster to datacenter as standalone host
Remove Host from Inventory