Not sure why it is so hard to show signal strength of bluetooth devices on a Mac nowadays, but...
HOLD OPTION KEY and PRESS THE BLUETOOTH ICON and HOVER OVER THE DEVICE YOU WANT TO SEE
The signal strength is not real time updated, so you'll have to do the same steps to get an updated value.
zzzZz Thanks Apple zzZzz for complicating this. Makes me wanna sleep zzzZZZzzZZZZzz.