Judging by personal visceral experience, my view is that brexit voters hate foreigners, and the vote has provided a platform for a greater and more visible and less ashamed expressions of that hatred.
Leaving aside that all of the 'reasoned' arguments for brexit as in economics, sovereignty, borders, fish (!), laws or whatever have been shown to be false what seems to be left is a raw hatred of foreigners.
The visceral level for me is to do with my family. My wife is Chinese, my son born in Lewisham hospital is mixed race. Prior to the brexit vote he would probably get racist abuse about twice a month. Immediately following the referendum result he would be abused at least once a day for about three months, then things settled down to racist abuse three or four times a week.
Additionally on his commute to London Bridge he would intervene in racist abuse incidents regularly. Brexit empowered this change in our experience in my view.
One memorable incident (shortly before covid) was meeting a bloke in a social setting, shaking hands, chatting, and then the man became curious about my sons different look. When my son said he was half Chinese the man got hand sanitiser out, made a show of using it, then turned his back ghosting my son.
This is in tolerant multi cultural London. I dread to imagine the experience some other have elsewhere.