Trying to get my sound through my av receiver from my new tv. Worked fine through an optical line and my cable box but cutting the cord and going to You Tube TV through Roku. Tried optical and nothing. Receiver does not have HDMI arc . Has 3 HDMI in and one out. Thinking maybe I need a digital audio converter box?

Try changing the audio settings on your Roku. Set to stereo to see if that gives you sound.

Optical out from TCL television to optical in on receiver is usually more reliable and less problematic than ARC anyways.  Not sure why an optical connection to your receiver is not working, especially if you had it working before with cable box.  Was cable box connected to receiver directly with optical cable, or via the optical out on the TCL television? Had you previously used the optical out on the TCL television?  Model numbers for television and receiver might be helpful also.

I had the optical running from my cable box into the receiver. Just got the TV as I had an old plasma display that did not have a tuner. TV was 15 years old and time to upgrade. My thinking it was going to be plug and play optical through TV to receiver. Have same TV in another room and have that going to sound bar and works fine. Onkyo HT 5100 5.1 probably 15 years old too. Not sure on model of TCL. Will post later 55” with built in Roku.

It is true that optical is mostly settings-free, setup wise.  From your description you have at least verified that the optical input on your receiver is working when you were using your cable box.  Are you using the same optical cable as you had previously connected from the cable box?  Have you tried another optical cable?  With the optical cable plugged into the TV, do you see light coming from the other unconnected end of the cable? In your TV menu Settings, Audio, what do you see with Auto Detect? And of course, are you switching the receiver input to the input source for the optical input?