Are you asking for recommendation of a universal remote to get or do you have one already and want help programming it?
Can't help if its the latter don't have the specifics of what universal remote you have?
If its the former I would recommend the Inteset 422-3, its 4-in-1 remote has preset codes and is a learning remote. It will give access to discrete commands through the use of Advanced codes(EFC) which are 5 digit codes for individual function like Disney+ command on the roku.
I need to hook up a universal remote to control my Xfinity and the Roku. Please help.
If you mean a roku TV, the xfinity control will power it on and off and control volume, and you lose a lot if you use anything else (voice commands, and RF non-directional control). Also note that you can use the xfinity app on a roku as a substitute for an X1 cable box so you might manage without the xfinity box/remote (changing channels is awkward with no number buttons, though).
You can use a harmony for basic operations of both including switching inputs on some other type of TV.