iphone could not be updated error 14

I'm trying to update iPhone 6S to iOS 14.4.1.

I get this error message:

"iPhone could not be updated. An unknown error occurred. (14)"

Tried twice. Same resulting error.

Anyone got suggestions as to why this might happen? I just successfully updated an iPhone 8 prior to plugging in the 6S.

iTunes 12.9.5.5, iMac 27 inch running 10.14.6 Mojave.

Thanks!