Big Sur bluetooth keyboard lags and misses keystrokes

OS 11.2.1 on M1 Mac mini : the Apple wireless keyboard keystrokes are not being processed and displayed immediately when connected by bluetooth. In order to get proper response, the keyboard has to be connected with the charging cable.

Also, the lag between keystroke and display can be so long that some keystrokes are not being processed or displayed. E.g., when I typed "bluetooth keyboard is very slow" into safari's search window, I eventually got "bluetooth keyboeryslow".

I am also getting (in Safari) a list of "accent marks" pop up above the partially displayed keystrokes. Never had that happen before and didn't realize there was a pop up window for accent marks.

This occasionally happened prior to OS 11.2.1 but is now perpetual.

I've had the keyboard for a couple of months.

Removing the keyboard from the list of bluetooth devices and reconnecting changed nothing.

Turning the keyboard on and off changed nothing.

Changing the response times in System Preferences under both Accessibility and Keyboard changed nothing.