I have a 2021 gle 450 with 20 X 9" rims. The stock tire size is 275 50 r20. Has anyone experimented with different sized tires on this model. I would like the taller/wider more aggressive look of a 285 or 295 tire. But, I'm unsure if that is too much tire on a 9" rim width.

 

In instances where I have tried to bump up a tire size, I have always experienced a loss of handling, but I have a small sample size (me).
Check each tire manufacturer's size charts and make sure that you are within the acceptable range for your wheel width. Preferably smack in the middle for best results.

 

You might try a search to look at threads on the subject. There is a lot of technical info. There are several issues besides what tire size will fit on a 9” wheel. The sizes mentioned will probably fit on a 9”. Discount Tire has a range fitment chart.
Your wheels have different offsets if you have the AMG exterior...et57 front and et44 rear so don’t mix up the placement.
A larger tire will make for a different speedometer reading.
Larger tire width=more sidewall bulge that will ride better but will “sway’ more in corners. Only noticeable in aggressive driving.
Wheel well clearance in front could be an issue turning. The second number in the size is a % of the first so you might have a wider tire.
Here’s a calculator you can use.
http://www.rimsntires.com/specspro.jsp

 

That's good general information, and a place to get started. It's a great way to visualize various rim and tire sizes.

@fmi1 just be aware that there inconsistencies between tire manufacturers, and a 275/50R20 (or other) will likely be a different size from different makers. Best to check the individual manufacturer's site to ensure your candidate is listed as appropriate for your rims.

My experience is that the wrong size tire can be very noticeable in normal driving, and if you are sensitive to your tires, can be quite disconcerting.
An example - on our C240 I went from 205/55-16 to 225/50-16 (both sizes listed on the door post, manual and various vendors) and my wife hated the result. She said it seemed "squishy" and "slow to turn," no matter what pressure we tried. I hated the tires because the car completely lost its sporty feel, even on runs to the store. It felt more like a Caprice Classic than a sports sedan.

If you are just looking for a "look," then none of this will make a difference, but if you want to preserve feel and safety, there's more to the equation.

And to @Ron.s 's point, that sidewall bulge is mostly used to achieve the correct inflation pressure, after you have the proper size tire. If the tire is the wrong size for the wheel, the "bulge" won't even be visible. (If I understand what "bulge" means in this context.)
I also agree that clearance to suspension parts and fenders during full suspension travel and steering lock, is a consideration if you go wider or taller.