What do you struggle with the most about backgrounds and environments?

Backgrounds can be very daunting especially if you are not sure what to have as a background to begin with.
I believe what helps the most is to approach it not to dissimilar to character design. That is, you put some thought into the background, how it looks like and why. If its an abstract background, maybe it should push forward the main drawing and add a bit of mood. If its a fleshed out environment, consider putting thought into constructing a compelling scene with it.
In the context of a comic book, its best to always plan a background with your panels and not have it be an extra for the characters to awkwardly float within. Plus, putting that little bit of extra attention into the environments can help you really immerse the reader into the world. It does not have to be expert-level immediately, even a small amount of consideration can make a world of a difference.

I've picked up a couple of tutorials to help some people get started on adding backgrounds for their work.

https://www.youtube.com/watch?v=Unau9KHn8Xg
https://www.youtube.com/watch?v=pmdc2zQ9jvM

Perspective. And also scale. More often than not I'm like, "Wait, this figure doesn't look like it fits properly in this space."

Sometimes perspective, but mostly I struggle with nature, architecture and nuance in my background artwork.

I'll definitely be making a guide for perspective! That's something a lot of people seem to struggle with, especially how to apply it to panels. I find Framed Ink series books to be fantastic for this! It also helps you learn paneling as far as frame by frame. Amazing series. Thanks for the suggestions!

Colors. I have retinitis pigmentosa, which basically means I’m slowly going blind and color blind. I struggle more with seeing color than anything. Right now it’s tolerable, but when it comes to making backgrounds, it’s a tedious and difficult process. I’ve been trying to learn how to desaturate my backgrounds from not being too vibrant, as the world is pretty dull, but then it’s difficult for me to tell if it looks ok.

I want to be able to have a huge well-planned out environment like in video games but I dunno how to draw maps and even how to place architecture to make it look right. Not only that but drawing a building from multiple different perspectives is hard for me.

This might be too much advice, but I would encourage any artist to try out Blender 3D.
It's very daunting to learn for a novice, but if you learn the hotkeys/navigation/GUI, it can be a valuable asset/resource to use.
If nothing else, you can make some cubes on a plane to simulate an environment and use it as a guide for perspective/scale.
Blender.org and YouTube are good places to start as far as how to use.
(I hadn't updated my own version since ver. 2.7, so plz don't ask me, lol!
There's also no 3d mods in my current comic yet, so if everything looks wonky/off, that's because it is XD)

Perspective and also continuity. Sometimes I don't pay attention as much as I should to the little details, like for example that the same tree or rock can be seen in multiple panels in the scene

Backgrounds and environments are extensions of worldbuilding. Considering how underdeveloped my world is currently, I struggle to make evocative imagery in the backgrounds of comic panels. I also struggle with the proportions of stuff in the environment, like trees compared to the mountains...

I struggle with adding enough detail and mainly lighting. My art style for my comic Room For Four has a style where I try to render it more realistic. If that makes sense. So getting lighting to look good in the background, especially when it’s blurry, is hard.

I think one of my biggest struggles with backgrounds is trying to make them not look boring and empty. One trick I've started using is hiding jokes and easter eggs in the backgrounds. One page of Rewrite History has a store that references name of a song title, and another has a character that becomes plot relevant later hidden in one of the wide shots. Little things like that help make it feel like I'm not just failing to draw cubes in perspective with every background.

I have trouble with buildings.

Detail in the background is also quite challenging and to keep it consistent.