I would put one nice big piece of moss picture right in the middle of the wall in order to upper light "lights" the variability of moss picture. The question is if it should be in black or natural frame. If natural, then, some natural bowl should be on the high furniture. Or tight wooden lamel wall with occasionaly hacked hanging greenery.

I would first want to know what kind of business & do you have free rein regarding what you can do? i see you have a few live plants in there, that’s good. I would add a taller, easy care plant, such as Sanseviera (snake plant ) on the lower bookcase maybe. Since I hated the flourescent overhead lighting in my office I had some of the tubes removed & i replaced with softer lighting, but this might not be a concern for you. Nice, good sized art in colors you like will help a lot. Framed photos of whatever you love ( family, pets, travel pics, etc. ) will help personalize your space..

Is this the reception area? we don't see much of the space, post more photos showing all 4 walls.

Big art, at least 24”x24”. Go big or go home is my motto.

Looks like a business, so what are you allowed to do on that back wall? And what do you want to convey (young/edgy, calm/peaceful, high-end professional, etc.)?

There are tons of large art canvases on Etsy and Anthropologie - they are nice bc they are well priced and very light so easy to hang

With that type of wall material you may need to get permission for hanging art, and then use the correct type of hangers.

Art but we need a bit more info from you. I do not consider 2'x2' art large but I do not know how big the wall is .It looks almost like a reception desk so we need that info you have been asked for.

Everything is very gray, gray floor, gray walls, gray desk. A few ideas... find art that you like.

We wait for more info.

Wall art is always provides a nice ambience to any space.

I would want something from nature that gives depth. I like travel posters.

We have this canvas print from greatbigcanvas.com in a very large size. You can see it in our living room pic attached below.

Find a subject matter local to YOUR area.

Thank you for your help so far, I’m uploading a few more pictures. Any design suggestions would be so helpful also. I like a more calm aesthetic. Maybe with groupings of smaller art?

Patricia asked some important questions. What kind of business are you in? How public is the office? It seems like a reception area. If you work for the Sierra Club, then you'd want some gorgeous outdoor photos--Ansel Adams comes to mind. But maybe your company makes cement???? You say you want calm, but the gray is more dreary than calm. You could do a large mural.

A larger art work or two large pieces will balance out the dark office furniture and set a mood better than smaller groupings. This wall mural shown in an office conveys a calm mood and isn't distracting. Sorry, the photo won't download, but it ticks all your buttons.

https://wallism.com/us/product/oB09Gq1q8nG0?utm_source=google&utm_medium=cpc&dema_id=19188642628&utm_content=&utm_term=&gadid=&gad_source=1&gad_campaignid=19188730768&gbraid=0AAAAApECfi_dc9a2lHTke9hvrX82oyG8x&gclid=CjwKCAiAzZ_NBhAEEiwAMtqKy3Th1nIwfTbjnyo7PNCKCIsgzu-f3kIG6EW0sDIZ-vVeo5br_JLGthoCN5wQAvD_BwE

More pics are not helpful with no idea about what the space is and what kind of business if this is a reception area.

Sometimes it’s hard to make fussy small pieces look professional. That’s why we’re recommending big sophisticated art pieces.

This reminds me of a supervisor I had many years ago. We were setting up a couple of new offices from scratch and I was ordering all new. I remember him saying we need to emphasize PROFESSIONAL. ”Pink staplers don’t belong in offices,” he said. A small thing, to be sure, but it got his point across. No cutesy pictures of kittens or ponies, little shelves with knicky-knackies, frilly lamps, or a basket with ribbon trim to hide a kleenex box.

I guess we are no longer needed .

Or she didn’t like our advice.

I thought of one more office-decor-experience I had. We employed a fine, highly intelligent and capable young woman in our business office many years ago. We thought we hit the jackpot with her. Until the day she brought in a stuffed cat in a basket, battery operated so it appeared to breathe and purr, and set it on her desk. How inappropriate is that? I’m retired now but when I see her, that cat is the first thing I think of.

OP might just be busy.