Listening to 5.1 Sonos on headphones and others listen directly through the speakers

There are a few options each woth own challenge.

You could group a play 5 with the 5.1 and connect headphones.
Plug the headphones (either long wire or wireless) directly into the source (bypass sonos).
There’s no officially supported means of doing what you want and the various workarounds may introduce lip sync issues to varying degrees so depends how much this would bother you?

There may br a few more workarounds but those are the ones that come to mind from previous discussion of this topic.

PLAY:5 Gen2 doesn't have a headphone outlet, only Gen1.

You could split the optical feed from the TV, sending a signal to a wireless headphone transmitter as well as the PLAYBAR/BASE. There are some wireless headphones which can accept Dolby 5.1 and there are some 5.1 headphone converters available. If you were forced to set the TV to output PCM stereo the speakers would forego the benefits of 5.1.

I think you should investigate whether your TV will play through its own headphone socket and optical out simultaneously. If this is required for TV sound I don't see much benefit in involving Sonos at all for the headphones.

I think you should investigate whether your TV will play through its own headphone socket and optical out simultaneously.
Yes, that's an option, perhaps into a Bluetooth aptX Low Latency transmitter. It does of course require the TV to have a headphone socket. Many modern ones don't.

My tv unfortunately doesn’t have a phone socket :-(That's a shame. You could maybe pick up a second hand ZP80 / ZP90 / Connect and use the output on that to a Bluetooth base station for headphones, but the lag issue would be the same as for a gen 1 P:5. In the end, Sonos isn't designed for headphones and nor is your TV, so it isn't really surprising that it is hard to make that work.