How do I fix black and white screen on iPhone SE 3rd gen?

You probably have turned on the Grayscale Color Filter Accessibility setting. Go to Settings > Accessibility > Display and Text Size > Color Filters > Turn off.

Bibi1724 wrote:

Turn on this setting did not solve the problem unfortunately

Then try going to Settings > Accessibility > Zoom > Zoom Filter > Off.

Bibi1724 wrote:

ok; this indeed resolved the problem and I noticed that the filter was set on grey shades.

Thank you very much

You are most welcome, and glad my piece of advice worked!

Bibi1724 wrote:

ok; this indeed resolved the problem and I noticed that the filter was set on grey shades.

Thank you very much

Great! You are very welcome!