Problem:

Trying to add a physical adapter to a virtual switch shows the following error: There are no free physical adapters to attach to this virtual switch.

Probably you have the ESXi Version 6.5 and Client Version 1.21

Solution:

Update the ESXi Client version 1.24 (or latest version)

• Download the version from this link (Sign in first to VMware)

http://download3.vmware.com/software/vmw-tools/esxui/esxui-signed-6360286.vib

• Move the .vib file the data store.
• Run the following command on the ESXi host: esxcli software vib update -v “datastore path/filename.vib” See image below.