Yes, xDrip supports Dexcom ONE sensors from 2021.
Please use the latest version of xDrip and follow the installation instructions for the G6/ONE sensor.

Although the manufacturer has set the lifetime of the sensor to 10 days, you can extend the lifetime if you use the xDrip app.
To do this, you will need to carefully remove the transmitter and wait at least 10 minutes, then attach the transmitter back to the sensor and start the same sensor as new.

The lifetime of the sensor is individual and depends on how well the sensor is attached and whether the patch will hold.
Some users prolong the sensor for up to 5-10 days.
That makes a total of about 15-20 days.

Dexcom ONE is officially available only in listed European countries.
More information can be found on the official website.

As far as we know, there is no such possibility.
Alternatively, you can use the xDrip app.

xDrip is an open-source app that allows you to connect sensors from different manufacturers.
More information can be found here: xDrip+

xDrip has a very wide range of features.
Low and high blood glucose alarms are one of its features, you can set and configure them yourself.

Yes, the latest versions of xDrip support NFC readable Novopen Echo Plus.
This allows you to record your last injections directly into the xDrip app. The xDrip then predicts your blood sugar movement a few hours in advance, use with caution.

Official xDrip group on Facebook
In this group you can ask questions and ask for help from other users.