SQL Server licensing (PDF license guide) requires that you license all cores (all cores installed on the physical server, or all vCores visible in the VM), up to the max limit of the SQL Server edition. In the case of SQL Server Web Edition, the enforced CPU maximum is the lesser of 4 sockets or 16 cores.
If your server has 16 cores, SQL Server will use all of them, and you must license all of them1.
If you need to increase compute on your server, you will need to do an edition upgrade to move to a version that supports more than 16 cores.
1 There is a deprecated feature that allows you to set CPU affinity to restrict SQL Server from using all cores. However, in addition to being deprecated, and causing unwanted side effects, it does not affect licensing. Even with CPU affinity set to use less than all cores in the server, you must still license all cores in the server.
select scheduler_id,cpu_id, status, is_online from sys.dm_os_schedulers
– Hiren Parghi Sep 29 '21 at 11:50