There’s several things here.
First, with a PLAY:5 gen 1, you have to be sure that your 3.5mm jack in use on the back of the PLAY:5 is the line in, and not the headphone out jack, the PLAY:5 gen 1 has both.
Second, you need to be sure that the 3.5mm cable is carrying a line level input, and not an input from a volume controlled output like a headphone jack on the T.V.
Then, you’d need to follow the suggestions at https://support.sonos.com/en-us/article/use-line-in-on-sonos
Finally, because this is an analog line in, there will always be a minimum of a 75 ms delay, which will make lipsync challenging. There’s a reason why Sonos came out with speakers designed to be connected to a T.V., the Sonos PLAY:5 gen 1 is absolutely not one of those purpose built speakers.
Thank you for your valuable time Bruce!