There are many approaches, depending on what broke. In my case the system was fine, just xorg being completely borked. So I logged into the console and fixed it.
If regular console doesn’t work, something really went bad during boot, for which there’s single-user mode which is kind of similar to safe mode from Windows 98 (I’m sure there’s something similar in newer windows versions).
And of that doesn’t work, there’s the minimalistic rescue shell.
And if that doesn’t work, you can boot from a USB or some other external media and try to fix your system from that, maybe even using chroot to use the system somewhat normally.