It seems that Southgate decided to stick to his plan to score first and then play cautiously, defensively, but now I think his plan started to fail, because for the first time Serbia started to have some moments that can be called at least a little dangerous. Of course, I want England to play attacking soccer, but for Southgate the result is probably more important than a beautiful game.
Nevertheless, Serbia still have chances, because one goal can always be scored, but if England score the second goal, they will probably win the match with 99% probability.
It finly worked for him as England played more of defensive game in the second half, and it didn't tell good on them. If not for their goalkeeper Jordan Pickford that saved their ass and denied Serbia some chances of scoring.
Serbia took over the second half and pressured England till the end of the match but they were unlucky and could not find the back of the net throughout 94 minutes. Bellingham only goal in the first have made a difference and gave England their first win in this competition.