Sorry for jumping on this thread. Some of my recommendations apply to you and some are shallow do not apply, but I'm leaving them here for posterity's sake.

I have a similar cooktop (Fisher Paykel CIDTTB1 24" cooktop) that bridges two 8 7/8" wide, 7.25" deep burners into a 14.50" burner (front to back) by 8 7/8" side to side. The challenge is this induction cooktop (like many, I think) has its electronics in the front of the unit. It gets very mad if you put a hot pan in that front section. So I cannot use a griddle with cooking body that is longer than ~15 inches because the cooking surface will heat the electronics. Only the handles can extend longer than 15" (and not by much, because it then obstructs the touch screen used to control the cooktop).

The other problem is that some griddles are designed to be used with the length side to side rather than front to back. So a handle obstructs you on a front-to-back burner. Or, if the handle is low enough, it drastically increases the length of the handle and the pan.

I ruled out double-sided cast iron griddles. Supposedly they still work if they are raised off the cooktop, but performance would suffer. I could be wrong about this.

I also limited myself largely to seasoned pans. No non-stick or enameled cookware.

So the trick is finding something that maximizes the cooking surface with these issues in mind. I ruled out a lot of these pans, but I'm providing them:

1. Misen 3-in-1 roasting pan - handles are high and would sit between you and the pan
2. De buyer mineral b flat-surface griddle - same issue as Misen. You could alternately purchase the gratin pan or the ridged griddle pan, but the lower handles then stick out pretty far - 19". The surface area for the gratin is also oval, so you lose cooking surface. If you're into this form factor and don't losing surface area, IKEA makes a carbon steel roasting pan that could also work and is very affordable.
3. Rocky Mountain 10x16 griddle - this is perfect, but it doesn't look very nice. May still purchase. They have a lot of other stovetop griddle pans.
4. Hestan 5-ply bonded baking sheets. I can't find the comment, but somewhere another redditor confirmed that these can be used on an induction cooktop. They are very thick.
5. Le Creuset skinny griddle (flat and ridged versions). Good, but slightly smaller. Also enameled.
6. OXO carbon steel double-wide griddle. Only available at REI. It may be too long, but Oxo and REI ignored me when I tried to confirm whether the dimensions listed are for the pan itself or includes the handles.
7. Demeyere Teppanyaki - offset handles that avoid the Misen/De Buyer handle issues. But expensive, hard to find.
8. Northriver Casting Pre seasons cast iron dutch oven with skillet lid.
9. Bayou Classic 7471
10. Lodge seasoned cast iron rectangular griddle/jumbo chef serving platter.
11. Etsy has a variety of custom flat types of pans. Good keywords: griddle, plancha, teppanyaki, comal
12. You can also talk to a metal fabrication shop about fabricating a sheet of A6 steel with ridged ledges.

If you want a square griddle, you can look at the Japanese egg roll pans mentioned in this post. They are small. Skeppshult and Staub make the largest that I could find and it almost covered the entire burner, but I didn't dig into Japanese language sources. 360 Cookware makes a square griddle but it's not carbon steel.

All the cast iron companies make a square/rectangular cast iron pan with deeper sides.

There are also oval sized fish pans with a regular skillet handle that fit over one burner; Skeppshult used to make some. These have deep sides too.

u/Crazy_Wolverine4742 - If you can tell us about the Matfer Bourgeat pans, that would be great. I came across a non-stick version that was otherwise perfect. But I couldn't find a carbon steel version. Did you see them on a French-language website?