Which smart treadmill would you recommend that supports zwift without footpod? And does automatically change the inclination when the altitude changes on zwift?
Here is a list of supported “Smart” treadmills: https://support.zwift.com/en_us/supported-running-hardware-SycvahzDB
No, Zwift cannot control the speed or incline of the treadmill.
I use a “dumb” treadmill (ProForm Pro 2000) and just use Stryd. This might be a less expensive and believe it or not a more accurate way to connect to Zwift. Another good option would be NPE RUNN.
My advice would be you are going to be paying a large premium for a smart treadmill and it just isn’t worth it, they aren’t smart enough to justify their premium - none are able to change speed or incline on Zwift.
A non smart treadmill plus a run pod (Zwift or Stryd) is a great option as they both give pretty accurate pace and cadence. Then all you need is a HRM and you are there. Combine this with an iPad or Apple TV 4k and a monitor and you have a way smarter treadmill which doesn’t have all that extra electronic gadgetry which you just know is going to die or become unsupported in the future. It is worth looking for something that will support a tablet or that you can fit a bracket for a tablet to.
So use the extra money you would have spent on a smart treadmill and get the runpod and tablet instead.