There might be a time when you start your render and the image is extremely dark and the exposure is locked? This can happen sometimes when adding a new model to the scene or the settings are off. Don’t worry, it’s not a big problem. Below you'll find some easy steps to follow and get you back to your work.
The VFB (Virtual Frame Buffer) shows the exposure is locked. As shown below.
Simply open the Render Setup - Camera - Exposure and try to change the EV (Exposure Value), if nothing changes then do the following.
Go to Effects and Environment (or press 8). Under Exposure Control click on “no exposure control.”
Now you are free to adjust the exposure from the VFB. Try to start your render again, then you can change the EV (Exposure Value) to whatever you like.