Some inspiration photos:

Custom shelf entirely across the nook:

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Go to consignment and antique stores. Mid-mod furniture is not that expensive.

https://www.wayfair.com/furniture/pdp/george-oliver-libre-d-240-e-l-shaped-writing-desk-w010196552.html?piid=842986800

Also available in Canada

https://www.wayfair.ca/furniture/pdp/george-oliver-libre-d-240-e-writing-desk-c010051579.html?piid=1784301284

I would go with lighter Scandi desk and chair, I would also consider lightening up that drab honey colored panelling. You could paint just an area of it around the desk area a cool color like apricot, sky blue, celery, mauve, cream color. I would add a pretty plant or two ---hanging basket above window.

Great spot - i’d go with a sleek and bright white desk against the wood paneling - Ikea has lots of options

Does the desk need to be a piece of furniture? You have a good set up to do a built in desk.

To get the maximum/perfect length, if handy have a wood slab cut to size, sand, stain and fasten to walls and with the money saved, get a great MCM chair and art (for wall on left).

Maybe look on Etsy.

If not interested in doing a DIY and not in a hurry, try Marketplace. I found this ad in minutes.

Random thoughts:

- I'd go down to Ikea and choose a wooden countertop /cut it into a wall-to-wall built-in desk. With the window above it, it'll be great. With so much wood-tone, consider painting it a pale color.

- I'd remove the current white curtain and add a glass shelf (again, wall-to-wall) for your plants. Maybe two shelves.

- Add a set of Ikea drawers-on-wheels that can slide under your desk /provide hidden storage.

- Place a sconce light on the left and right walls -- nice bright bulbs.

- And finish with a chair in a pale color to match the desk slab. But print to hide the inevitable dirt /stains.