SOLVED! noticed upon bootup a red MANUFACTURING icon plus "Manufacturing mode: to return to normal mode press Alt F at bootup". Remote laptop was not successful; but entring Alt F  on the laptop's keyboard immediately stopped the constant fan.
Owned laptop for several years. Now suddenly the fan never stops running, no matter how few apps are open. Temperature is normal. Ran SA (SupportAssist) Fan test, it failed. It is out of warranty for 2 years now.  The fan noise is so loud it interferes with hearing zoom audio. Ran full Rkill Malwarebytes Super Antispyware scans and McAfee scans already. Thanks!
XPS 15 7590, fan won't stop running, failed SA test