I noticed a Reddit thread talking about how our smartphones became the ultimate dopamine delivery system with making sure that you would look every X time at your phone and creating an addiction by making sure the phone would become your primary dopamine source and while they gave zero scientific research about this I must say... in my particular situation it felt very real and could attribute to my lack of focus.
So I now started to put the phone away at an inconvenient location at 21:00 and start to read, make a puzzle,... again.