Without looking at it it’s probably making a unique request to a resource on a NextDNS subdomain and watching where the request comes from. Like pulling an image from (unique _string).check.nextdns.com. This requires nothing special on the client, it’s making a standard request, and as part of that it needs to do a DNS lookup.

If the source of the and your IP are similar then it’s likely the same network, otherwise it can correlate the source with known resolvers.

I use HASS.agent to help manage my Windows desktop and expose various sensors to HA. It can suspend or hibernate the system. It does use MQTT as its connectivity plane.

You get easy access to their addons with a VM (aka HAOS). You can do the same thing yourself but you have to do it all (creating the containers, configuring them, figuring out how to connect them to HA/your network/etc., updating them as needed) - whereas with HAOS it generally just works. If you want that control great but go in with that understanding.

BTRFS has RAID built into the file system - instead of using MD you use BTRFS profiles which tell the system how to handle data.

For instance

• file system data (critical for the file system to function): raid1c3 which means 3 copies of core P file system data on 3 different devices
• user data: raid1 (so duplicating all your data on two different devices)

With this set up you could lose one device (of n, the total doesn’t matter), and not lose any data, and still be able to boot to recover with too much hassle.

BTRFS does block checksums, can scan for bit rot and recover from it, and generally tries to make your data safe. It technically supports raid5/6 for user data, the issue is around unclean shutdowns and a potential write hole where you could lose data, but if your system has a UPS backup and is on a relatively recent kernel it’s not any more dangerous than MD raid5/6 as I understand it.

The phone or browser may be using DNS over HTTP (aka DoH), check if you can disable it for the wifi network. You may have to disable it on the phone or browser to get your desired behaviour - look up directions for your browser.