I think lazy_gardens' idea w/ the closet from the office is to break through the back of the closet, from the laundry area (and wall it in on the other side). Then you'd have just "flipped" the closet from one room to another. I'd also suggest you combine it with the laundry-room closet to go the full length of the room. And so maybe instead of having a closet there, you'd just have moved the wall over by the same distance as the depth of the closet(s). That opens up the room by the full depth of the closets--and you say that's a pretty deep closet (I'm guessing it's the depth of a regular clothes closet--so, 24" easily. Can you stack that washer & dryer? They're built to stack, I think--and you aren't using the space above them right now (though you'd have to give up the drawers below--do you truly store that much in them? You might find it worth the switch). That would free up horizontal (floor) space by "building up" (the NYC solution for everything: skyscrapers!). That would make more "maneuvering" room, and create a place to set boots in the winter. And can you move the slop sink into the garage? That would free up that space as well, plus make it easier to make the laundry area look a little nice.

I'd like an office that changes usage over time. In My life, I had a large U shaped desk that took care of my ranch, my personal stuff and my work stuff. I've left my work for others self behind as I got older and ditched one side of the U into a large L shape desk. I also took down about 6' of upper cabinets. So, now I'm into gaming online, various projects including my 'cottage in the woods', my personal stuff as well as the ranch. With the cottage, I'm building my own 'office' again utilities about 8' of wall space in the living area. I need to function for personal stuff, gaming and gardening. I have two 27" monitors as well as a ton of equipment including printer, landline phone, router, wireless as well as hardwire technology, UPS, backup unit, to house and a place for office supplies and file cabinet. I'm also thinking about adding in a shredder. Where do I begin without turning this into a monolith?

You could add bookcases to the back wall, but you don't have to. Really to define the space we might suggest a larger rug so that the entire desk and chair fit on it, along with some filing cabinets or bookcases behind it. Below are some ideas for you from a few office designs of ours:

What about an adjustable table base that you can attach a nice top to? Could be nice wood or marble or granite, copper tray, etc, either square, rectangle or circle? https://tablebases.com/lift-base-black-stainless-steel-table-base-adjustable-height eta: oops not rollable...similar with a cheap top that you could replace: This is on $55 on the big river: adjustable half moon