Keyboard left-side Shift Key problem

Hello,
Sudden on-set after years of no problem.
I cannot type an uppercase (capital) Y using the left-side Shift Key. It does nothing, no space or substitute character. But I can type a Y using the right-side Shift Key or the Cap Lock.

See below when typing the first row of letters while holding the left-side Shift Key down:
QWERTUIOP{}|

All other letter/symbol keys work with the left-side Shift Key.
Same problem in all apps and browsers.

Mac Keyboard Ser# KY70100TUVZSA