The Roku probably thinks the missing remote just can't communicate because the batteries are dead.
Have you tried Settings > Remotes and devices > Remotes
You should see an option for your new Voice Remote Pro (in use). If you see an additional option, for your old remote, try clicking on it and then selecting "Forget remote" if it's offered.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X