From your bio, the vast majority of your Sonos equipment is old. It really is the ten years old that you refer to.
Older equipment needs to use the S1 app. But you’re right, you can’t mix systems - you might think about upgrading your speakers after all this time.

Name another manufacturer that would keep their speakers updated at ten years??

Indeed, old kit. But only now joined the community.

A Sonos device isn’t “just” a speaker, or even just a powered speaker. It’s also a computer, and the app is “just” a remote which is used to send commands to the speaker’s computer. To my mind, old WiFi circuitry and limited memory in older devices makes it tougher to support in a world with far more wifi devices and electronic devices in our homes (and therefore more interference) today than 10 years ago.  

Wasn’t it Bose that, a few years back, introduced a new product line overnight that was completely incompatible with their previous products? 

To me - and hence my observation - it seems odd to sign up to the community just to list bad experiences and announce an intent to buy alternative products. Most folk post their problems and ask for assistance from this user community. In the rest of my post I gave more information, to try to illustrate the challenge a manufacturer experiences when trying to support and maintain older electronic equipment in an ever-changing world. 

Moderator edit: Edited to remove reference to a deleted post.