

Most people expect a GUI interface to get into their desktop. But you dont have to use one if you dont want. SDDM can log into any desktops you have - KDE but also Gnome or XFCE etc. It can also help select X11 vs Wayland sessions.
There are alternatives like LightDM if you dont like SDDM. Or TTY is fine too. But generally they’re not large pieces of software and while they are undoubtedly bloated from what they could be, they are still small and lightweight in the era of Tbs of storage and Gb of memory. The savings you’d get in not using them would be small on the scale of the rest of the OS. Obviously they’re useless for none GUI machines / servers.
They’re called display managers because historically the concept was added to X11 system where you’d have a stand alone X terminal running locally for the end user with an X server which would then connect to an X display manager on a central machine. This was in the Unix days and shared spaces like governments, universities or corporations and the set up was potentially less hardware intensive allowing cheaper X terminals and an expensive central server.
The concept has gone now - PCs are vastly more poweful and can easily run the entire OS locally, and thin clients are the modern set up if you do want terminals/clients and central servers. The most common scenario is now the display manager running on your local PC, alongside everything else and essentially replicates the TTY login in a GUI form. So yes its basically a session manager but the name is historical and probably won’t be going anywhere fast.
It is an absolute crock of shit.
There is plenty of research on magnetism and humans and it doesnt need a new title and niche “research” from a frankly failed state like Russia.
We use high Tesla fields routinely every day worldwide in hospitals in Magnetic Resonance Imaging. Safety of this technology has been and is continuously investigated. There has also been extensive investigation of magnetic fields related to power lines and other use cases.
There does remain some uncertainty and controversy around potential effects of long term exposure to low T electromagnetic fields but its long established that short term exposure is safe.
This “research” is more on the realm of autism vaccine science. A lot of money can be made in niche fake sciences both in the industry of research itself and then the crap they can sell to ignorant people as a result.
Russia as a state has been systematically destroyed over the past few decades and most of its institutions have a terrible reputation now. While there are undoubtedly still good scientists in the country, they are working in a gangster state and many of the best minds have long fled for better opportunities abroad.