brightness problems with new app Locus Map

I tried to switch over from Locus Map 3 Classic to new Locus Map 4. The apperance of the new app is quite nice and I tried to install everything on my Smartphone Samsung Galaxy S21 Ultra. Everything seems to work well. But in practical use outdoor, I noticed that the brightness of the screen turned down in a few seconds to a level which cannot be accepted in practise by sunshine or even normal daylight. This never happened before with the previous Locus version. All attempts to control or readjust screen brightness via Samsung control functions failed. Under these circumstances the app Map 4 cannot be used. What to do??