I'm planning to buy a voice control remote but I'm curious if it will work on my Onn Roku TV?
Yes, it can be paired to voice remote, all Roku TVs can.
You can check by going into settings > remote & devices > pair a new device > remote
If you can make your way through the menu via the above it proves your model can.
I just received three RC-AL5 voice remotes from China, they have Onn Roku TV printed on them.