This is the wall I want to mount both TVs on. And this TV is the 55 inch.

65 inch

A dark wall will help, as suggested above. I would make sure to hang them centered to each other so the height difference is divided and not as noticeable. So, 2.5" difference on top/bottom.

Hang the 65" TV. Paint a 58" x 33" black rectangle adjacent to it. Hang the 55" TV in the rectangle.

"Does anyone have any ideas to help make this look nice?"

A room with two large screen TVs of the same or difference sizes (no matter) isn't going to look like a decorator's unique innovation others will want to copy. I think that would look odd no matter what. Hopefully it's a room not easily seen by visitors.

Can you get a piece of furniture to go underneath both, to kind of unify them a bit? A long floating shelf/cabinet would be modern and sleek. The piece that is there now seems out of place to me.

Is this going to be a "split screen" using one image spread over two monitors? If not, then I would put one in a completely different location. If it is, then I would buy another 65" one and be done with it.

Tacky.

I like the idea of a dark wall, and centering the smaller tv to split the difference in size.

An alternative could be mounting them with the tops at the same height and letting the game systems or decorations or whatever else fill the space under the smaller tv while leaving the area underneath the bigger one clear.

Not tacky. Perfectly understandable from a gamer’s perspective! I’d paint that wall a dark colour to draw the attention away from the tv sizes. We have one of our TVs hung on a dark teal wall and it de-emphasizes it.

IMO a gaming room always looks tacky so relax enjoy the space for what it is IMO get one long low cabinet and mount the TVs at the right height for gaming above it .

Is it possible to put the two TVs on different walls?

Here's some ideas:

Hang a few square floating shelves (not aligned to each other) above the 2 tvs. This would offset the tvs' malalignment and come off as intentional.

Hang the 65'' horizontally and 55'' vertically, so it seems that they have different purposes.

Hang the tvs each on a lighted floating wall panel, but decorate each panel differently.

Hanging a TV Vertically? Huh?

Why not, Stax?

If you were going to buy a new tv anyway, why not just buy another 65” so they match?

mtvhike

You would watch a 1080x1,920 image? How would you process a 1,920x1,080 transmission and display it on its side?

EDIT: Seems the OP posted and ran 29 days ago. lol