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)
- 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.

How am I performing this: “Move the .vib file the data store.”?
I am on a Mac.