All new wall ovens are shorter in height than older wall ovens
If your recently had a replacement wall oven installed , here’s some guidance on how to fill the gap at the bottom.
If you put a wood filler strip it will not look good, period, and will stick out like a sore thumb
Matching the cabinetry color is a big problem and is not cost effective, you'll never match the cabinet color perfectly, and even one color shade off looks terrible, don't even try it, just use a stainless steel wall oven filler strip
A stainless steel wall oven filler strip looks like it’s part of the wall oven and is by far the best option