Dictation occupying most CPU

I'm very surprised to see my Mac Pro (2013 late) becoming extremely slow ~ one week after my upgrade to Catalina... I thought some background programs were running and now I have to re-start my computer every day to boost the speed a little bit (which is very very strange). Thanks to Activity Monitor, I realized it's the automatic activation of "Dictation" (Voice control???) after the Catalina upgrade.

However, when I force quit Dictation from Activity Monitor, it is open once again. Then I force-quitted it, and here it came again. Then I went to search for how I can completely turn this function off so that my CPU or RAM can be released from the Dictation ****, it seems that there is a disable function in Preferences - but I am not sure if this can really turn it off. May I know if anybody also has similar trouble after upgrading to Catalina? (Especially these kind-of-new functions may not be very compatible with the old hardware...) Thank you!