Decimal Point on Numeric Keypad

In System Preferences Keyboard…

Bring up the on-screen virtual keyboard viewer (part of accessibility), and see what registers as a keypress, if anything, when the keypad period is pressed.

Also check for any shortcuts that include the period in unexpected ways, while you’re in the Keyboard Shortcuts secrion of System Preferences.

Reboot into Safe Mode—and reset NVRAM and SMC on the way there—and see if the problem persists. Some problematic apps can sometimes grab key presses.

Links to more info on what’s mentioned above:

https://support.apple.com/guide/mac-help/use-the-accessibility-keyboard-mchlc74c1c9f/mac

How to use safe mode on your Mac - Apple Support

Reset NVRAM or PRAM on your Mac - Apple Support

How to reset the SMC of your Mac - Apple Support

Try the following:

1 - Reset NVRAM or PRAM on your Mac - Apple Support

2 - How to reset the SMC of your Mac - Apple Support

Please reset the SMC 2-3 times back to back with all wired peripherals disconnected such as keyboards, printers, scanners, cameras etc. Please note the link below for instructions.

SMC Reset

Do you have your locale set for a comma instead of a decimal point?