There are no channels to change on AppleTV. But if you mean you want a remote that can also change channels when using other sources- such as a cable connection or cable-like streaming service- ANY remote (other than the AppleTV remote) will have channel (change) buttons.
In a typical universal remote, you'll have some "mode" buttons and one might be a button called cbl or sat (for cable or satellite). Put it in that mode programmed for
that source (where you have channels) and buttons like channel change will change channels. When wanting to use AppleTV, a typical universal mode is AUX or STM/STR, and then the buttons that AppleTV can process will work with AppleTV. "Change channels" is not one but "up" & "down" is often used when streaming apps with apparent channels present a DVR-like grid of "what's on".
And again, AppleTV can do something different than how we traditionally set up any universal remote. It can "learn" the remote instead of having the remote learn AppleTV. So you can buy (or may have) ANY remote- ideally one with buttons to control disk/vcr type buttons too- set up its AUX or STRM button for any old disc/VCR/DVR and then use the "learn remote" features of AppleTV tvOS to learn the commands the remote generates when you push buttons that work with AppleTV. Technically, a button you push might be trying to tell as Toshiba DVD player (you don't own) to fast forward, but AppleTV "learn remote" will (be taught via AppleTV learning to) "see" that as "fast forward what user is watching on AppleTV." Clicking menu on that remote might be an infrared command for that Toshiba player to go to menu... but AppleTV will interpret it as show the AppleTV menu. Etc.
As to HDMI ARC "stop working" (I'm guessing you mean CEC functionality), I'd work through the possibilities. Have you:
- restarted the TV(s) as each has its own computer inside that may have crashed? Restart here means unplug, wait a few minutes, plug it back in?
- upgraded HDMI cables as devices like AppleTV "like" latest cable standards vs. perhaps years old ones?
- checked connections to be sure wiring is correct, such as using TV HDMI in from AppleTV and eARC HDMI out to that soundbar?
- tried switching HDMI ports to rule out just one bad port?
- stripped out all links in the chain but just AppleTV and TV to see if CEC will work with those? If so, add one thing in at a time and test with each addition to see if some particular link "breaks" CEC. For example, add just the soundbar back in and check again. In other words, you are hunting for which piece of the chain is actually the culprit.
- subbed in other sources using the same AppleTV cable just to narrow in on if the problem is TV, cable or device? If another device works fine through the same cable, you'll know you probably need to check settings in AppleTV because it is very likely why CEC is not working.
- taken your AppleTV box to a friends house, temporarily connecting to their TV to see if HDMI CEC works with their TV? If it does, that would tell you your settings in AppleTV are right and your problem is more likely cable or TV at your home. If you take your own cable too, you can go ahead and test that out at the same time (theirs first, and then yours). If this points to your TV, try each HDMI port on your TV and, of course, go into the TV menus to be sure CEC functionally is turned on correctly.
The name of the game when some A/V feature used to work but doesn't now is testing through each variable to narrow in on where the actual problem lies. As is, it could be AppleTV, cable, TV, cable or even soundbar. When I see "stop working" I usually think a software update has altered settings that need to be put back to how they were or a standards update has overrun existing hardware, particularly cables. Sometimes, it's a simple as the dog or cat has chewed on the HDMI cable such that it still works but only partially. Sometimes, it's a power surge (lightning) has partially crashed some link in the chain's computing tech making some part not work right. Etc.
