why is my banana blueberry butte quickbread so gummy inside even after baking it for 1 hr 30 mins? at 160 degrees celcius. I used a oven thermometer

In my experience banana bread always takes WAY longer to bake than expected. With the addition of the moist blueberries, bake time gets even longer. Next time, I'd try nudging the heat up a little.

The picture is a bit difficult to see, but if the bread is gummy, that sounds as if it did not bake long enough. Did you really bake it at 160 C? That is about 320 F and I think that is too low. Usually quick breads and muffins bake at a higher temperature--perhaps 350 or 375 F--sometimes even 400 F.

I would compare your recipe to some others, perhaps in an ultra-reliable cook book. Check the recommended oven temp as well as the ration of liquid to flour and eggs--your recipe might have too much liquid for the amount of flour.

This is the picture of the bread