After recent update, Manjaro doesn't boot up to desktop theme

[Wollie]

@BIZDIK

I’m running Plasma.

You couldn’t provide less info. Why not sharing

$ inxi -zv8

@BIZDIK

I just updated in tty.

With what command?

Usually, it’s recommendable IMHO first to update just using pacman to ensure only repo packages are updated and your issue won’t be linked to any AUR package.

@BIZDIK

It seems that no matter how you update, whether through the package manager or TTY

Here you mix two not linked things:
TTYis only providing another environment, with the “package manager” you probably mean pamac GUI, if so please name it.

@BIZDIK

I’m not 100% certain, but I think that when I used the Manjaro ISO, it didn’t mount the boot partition (EFI system partition).

It’s always helpful to google a bit upfront, not really difficult to find:

[HowTo] Chroot from or into any Linux distribution

Difficulty: ★★★☆☆ Step 1: Mount your system. This works for both GRUB and EFI systems/installations Okay, the first thing to do is to be root. To do so, open a terminal and type in sudo -i then hit the Enter key. You may then give in your password if prompted. We then need to create a directory where we will mount the target system. In this case, let’s make a directory named “chroot”, by entering mkdir /chroot in the terminal. Time to find where is your system located!! To do so, you may e…

@BIZDIK

So now I’m left wondering: was that previous 2.3GB update that broke my system just a fluke? Or was it pulled back? What exactly happened there?

Try again to enter a TTY and tell us what

$ sudo pacman -Syu

provides.