You’re lucky, a Sonos One ‘surround voice assistant’ is disabled with the Sonos Arc & Beam - I would like the option to have it on one surround ...and to choose left or right.

What I’ve chosen to do for my Arc HT setup, is purchase an echo dot instead and put it near to where I sit, it just saves me shouting (sorry that’s an exaggeration on my part - I mean raising my voice) the length of the living room.
 

I would like to be able to select the voice assistant speaker in a HT setup… but I guess it’s a lot more development work/time to achieve this outcome - so my echo dot will do for me, as the next best option.

You could replace on e of themn with an SL……

I have read that if you unbond the One's, ad Google Assistant to only one of them and re-bond them as surounds, the One you previously had GA on will keep it. Not sure if this still works (or if it ever worked at all).

I forgot to add Alexa skill to the new, second sonos one that I added as one of the surrounds. Once I did this, mic’s on both sonos one gen 2s are active as surround speakers. Only one ( I guess the one that hears the Alexa communication first or loudest) of the sonos ones will be used as the dominant speaker that activates the sonos surround system to respond to the Alexa command. Problem solved.