Getting HDMI-ACR working initially seems to be a real PIA, and based on my searches trying to resolve mine, across many (most?) brands of TV's, and AV Receivers/soundbars.
I replaced a Visio 55" TV that was probably 6+ years old. Still worked fine, but wanted an upgrade, without breaking the bank. Hisense 65H8F fit the bill. 65" 4K well below $600.
I have a Onikyo AV Receiver, 7 speakers, works and sounds great. I had been using ARC via the HDMI cable to he receiver, works great.
New Hisense wouldn't see it, even had ARC grayed out as a speaker choice. At some point the ARC was active, but would immediately revert back to TV speakers. Everything I read in the manual, and found on several sites matched my settings. Also went into all settings in the Onikyo, looked like it should work, but didn't.
Turned it all off to stop for dinner, and it all worked when I turned it back on.
Same feeling I get when trying to setup printing on a computer.