Hard to say, it can come down to many things , heres a few…
Check your post process volume
Camera settings, specificly exposure
In viewport see if game view is checked
Check that the materials are setup correctly
Check all of your lighting settings…
Atmosphere, height fog, skybox, directional light etc
Something you did at some point will have changed it to be looking like this… or there’s a currupt file somewhere or last option you discovered a bug and copying the stuff not related to lighting and re making the lighting stuff is probabbly your only option