We can only guess. But they can probably detect contacts for which the phone number is updated or which have several assigned phone numbers.

I would assume that “market share” is related to the relative number of units sold/number of active subscriptions/fraction of total sales in terms in revenue, or some similar metric. I run a variety of different distributions on servers (bare metal, VMs and containers) and desktop computers. Do they all count equally? Without giving it more thought, I wouldn’t even know how to determine the market share of Ubuntu in my own home in a sensible way.

With Windows, I can just count the number of active licenses. Oh wait, its zero.

• Browser: I selfhost Piped
• Mobile: NewPipe works fine
• Subscriptions: I use RSS to subscribe to my favorite channels. No account required

This is just a frontend, DeepL (or any other engine you use) still sees the text that you translate.

Also Logseq.

The same applies for various password managers.

That does not sound plausible to me. Typically, your own computer would be behind a router that is either doing NAT or has a firewall (probably the former). Any incoming traffic would be directed to the router without any chance of reaching your computer. Whatever you saw was either outgoing traffic or incoming traffic in response to connections initiated by your own computer.

Connection attempts from the FBI? Could you specify that a bit further?

home assistant, freshrss (and a few related services such as rss-bridge), nitter and piped. I tried to host libregrammar, but ran out of memory.