EDIT: It seems this made it to HN. Is this my cue to Soatokify this article?
The NightOwl application has existed since 2018 and is used to automatically switch between light/dark modes on the operating system. It is an alternative to the built in macOS automatic mode which only switches when the user steps away from the computer.
However, the application has been bought out by “TPE.FYI LLC” in late 2022 that forcibly joins your devices into a botnet for use of market research, without your knowledge (other than the TOS in small text on the download page) or express consent (this feature cannot be turned off, even when the app is quit). This is documented in their terms of service.
Something being open source doesn't automatically make it safe to use. Sure, it means it's easier for people to check for security issues, but how many people actually have the knowledge and the time to do it? And even then, take the log4j vulnerability from a while ago, it's been present in the code since 2013 and only reported in like 2021.
You need to examine your devices packets and see what servers they're going to. You can do that through Wireshark on Windows, or use an external sniffer to examine them.
I'm not aware of any native apps for Mac that can do that, but maybe others will know.
This should be illegal by European law. Without further knowledge it seems like a prime example for the GDPR letter of death and a pretty solid case for data protection lawyers
Light and dark mode can be set to turn on automatically at a given time or can be set via sunset/sunrise. Not sure where you got people need to step away from their devices to enable.