yes tty1 was the intended result, allowing system to complete boot up
as I said , the isolate command will do a normal graphical start
the actual lspci output isn’t that interesting, what would be interesting is any differences between precompiled kernel and your compiled kernel, so take both lspci outputs and run diff -u old new, and I bet of you do that diff -u you will find differences for device 2d:00.0
the while boxes seem just like normal xterm windows, maybe with twm running as a window manager, maybe even focus follows mouse, very old school, and probably some sort of fallback setup, though if you are using startx you should check your ~/.xinitrc it will probably have xterms and maybe twm too. You should check you can move the mouse around, and get input focus and use the xterms are terminals.
why the xterm/twm environment is running and why plasma/kde is not running I don’t know, probably because kde is not in .xinitrc and xterm/twm is in .xinitrc.
so it seems to me that X is starting, but not the version that sddm is happy with
So cross check 2d:00.0, and that should give you a driver to hunt down, whether it is a precompiled driver, or you have to compile some special module for your hardware, maybe with dkms.
If you want to switch back from multi-user.target as the default then systemctl set-default graphical.target
Might be relevant too, or some hints: Error boot after nvidia update : Stuck on reached target graphical interface
If you find that you have already built the drive, then load it using modprobe and try sddm again. If it works, then you have to convince dracut/mkinitcpio to load it, although if it normally loads with the normal precompiled kernel, I don’t know why it isn’t loading now, unless it is something to do with secure boot and signed drivers.