If you download an ISO for a Linux distro for x86 and burn it onto a disc or USB stick, and put that device into the target computer and start it up, it shows an interactive installer.
If you want Linux on a Raspberry Pi, you have to use a special tool to put the files onto its "hard disk" in the form of a flash memory card, and then put that into the RPI, and then start it up. There is no installer; it goes straight into the "installed" OS.
This prevents setting up encryption on the RPI (since there is no installer), which has caused me to be unable to use my RPI for anything nontrivial. While it's technically possible (allegedly) to do encryption post-installation, I have been completely unable to do so and no online guides help.
But what exactly causes this? I think it has something to do with the lack of a PC/x86 "BIOS" on the ARM-based Raspberry Pi, but why can't there be an installer for ARM systems if they can make the entire Linux run on it? Is it quite possible, just nobody has put in the work to do so?
Is there something about the ARM architecture or the RPI specifically which technically prevents an installer? And is there any difference which version of RPI you have?