Old Yamaha Rx v373 - straight rarely uses centre channel?

Hi all,

Bought all my gear used so got an old Yamaha Rx v373 which is a decade old and a 3.1 setup. It connects to my TV via arc.

I'm noticing when leaving the audio setting on straight (rather than using sur decode to force 3.1) that pretty much most content only plays 2.1.

I've lately been using stremio and vlc/Nova player on my android TV. I notice that even on new content the straight function still only plays 2.1. Is this because the avr doesn't support the latest codecs and the software (vlc/Nova) forces it to play?

Thanks,