Well the answer is simple at least for v5,
We should save it into ctx.state
example
const user_account = await strapi
.documents("api::user-account.user-account")
.findFirst({
filters: { id: user.id },
});
ctx.state = { ...ctx.state, user_account };
Then if you load that middleware
you can access it via state
const userAccount = ctx.state.user_account;