My fingerprint sensor is a bit hard as well. My mother-in-law also has a Fairphone 3 and she has the same problems.
A few tips that makes things better:
-I found that pressing the sensor for a longer time works better. I had the habit from my previous phone to put my finger on the sensor and immediately taking it away. This sensor need to be pressed for 1 or 2 solid seconds to work better.
-You need clean and dry hands. The slightest layer of grease makes the sensor unusable.
-I clean the sensor once a week with the same piece of cloth I use to clean my glasses
-The less fingers you registered, to quicker the detection is. Try only registering 2 or 3 fingers.