I think it depends where you are. In some countries the recommendation is to switch to food first then milk but in other countries there is no guide like this.
I never switched to food first but instead switched 1 of the milk feeds to a solids snack with a drink of water, then later switched the other milk feed, leaving WU and BT milk feeds plus 3 meals and 2 snacks. I waited until my DS was less interested in one of his day time milks before switching it.