This is technically an Apple question. What you’re asking is ‘what does AirPlay 2 communicate across”. To the best of my “limited” knowledge, it sits on top of Wi-Fi, so the answer to your question is ‘no’.

This should be relatively easy for you to test at home, though, assuming you have the equipment. Just unplug your router, and try the AirPlay 2 connection, and see if it works. 

On the other hand, if the Sonos device that you’re connecting to can accept a Bluetooth signal, you have no real need for AirPlay 2 at all, and can just use Bluetooth. You’ve indicated that you want to get a non-Bluetooth enabled speaker though.

Would it be that challenging to get a simple travel router for this home? While speaker initial setup requires access to the outside LAN, once the speaker is set up, it can be run on a local LAN with no issues.

Bruce - it’s a good idea to try at home.  I will do that. 
 

the more I think of it, I will have reliable wifi in Mexico it just may not connect to the WWW reliably. If Sonos is just using the wifi as a bridge to connect, it might not matter that my internet service could be unreliable because the wifi will still work. 

Airplay needs wifi, but not internet per sé. Question is: where wil your music come from without internet access?

My hope is that at least my downloaded music would stream.  
 

we download a fair bit when heading to MX. Cell and internet not extremely reliable. 

You’ll be fine. I have a Sonos system in MX and it was originally on a very iffy internet connection, but could Airplay without issue. (Music came from phone’s data connection which was much better than our MiFi-based internet then). We have gigabit fiber there now so can stream from all the usual services these days.

You might need a solid wifi system though - our MX property is built of heavy concrete/rebar infused walls, and wifi across 3 floors was a serious challenge (compared to “cardboard-built” USA homes). Got an Amplifi mesh system, one device per floor (using Ethernet backhaul), all good now.

Thanks.
 

That’s what we did (are doing) as well. Ubiquity system wired into each room of each floor.

We hired a local who does this and he recommended it for the reasons you outlined. 
 

second question if any are interested in advising, is the Beam (gen2) a good enough TV Soundbar? Probably a 75” TV.  Before you say so, I realize the Arc is better but the price is a lot more. 
 

Thanks for your thoughts 

With a 75” the Beam seems small. Though I must say I’m using a Beam with a 65” myself.