I had an identical situation when I remodeled my kitchen. Even with the old dishwasher under it, the counter still flexed a little in that spot. Since I was installing quartz counters to replace the laminate counters, I didn't want it to be unsupported because quartz was likely to crack instead of flex.

My solution was a large L-bracket that extended from the wall near the dishwasher/oven seam. I ordered a 22" Universal countertop support bracket from CenterLine Brackets (link below). Quality was top-notch, but it did require me to cut open the wall and install 2x8 blocking between studs to give it something sturdy to mount to. I also had to precisely mount it to be level with the rest of the cabinet framing so the countertop would be level. It gave me just enough clearance on the back of my new dishwasher to put the dishwasher in without hitting the bracket.

https://www.countertopbracket.com/Countertop-Supports-Floating-Inside-Wall-Mount-p/fwm.htm

Here's a photo of it installed https://imgur.com/a/jao7Cmm