CPU Usage Incorrect in sys.dm_os_ring_buffers
Microsoft says that DMV (ring buffers) doesn't work on SQL Server 2017, only 2019:


  Sys.dm_os_ring_buffers DMV has been a key DMV used for monitoring SQL
  Server by built-in tools as well as third party monitoring utilities.
  When SQL Server 2017 was released on Linux, unfortunately this DMV did
  not return correct CPU usage information by SQL Server process. SQL
  Server team is glad to announce that the starting with SQL Server 2019
  release candidate, the sys.dm_os_ring_buffers DMV returns SQL CPU
  utilization correctly.