Also, how on earth MC's household is protected? He has no male servants, no guards at his place which is at the middle of desert. Sounds like a dream target for slavers to me.
Not really. You need to consider this from the perspective of a premodern power structure, which this kingdom is.
The MC is basically the retainers of the reigning monarch. A sort of knight in her service, if you will. More than that, he is clearly a very high ranked retainer.
We can see this importance not just in how close she allows him to get but in the various privileges he has been given including but not limited to the right to an independent household, the use of forbidden technology and the leeway to operate in her name and yet without a leash.
What this all means is that he and more importantly his position is going to be well known in society. And that in it self carries a certain degree of implicit protection. Because to attack him is to attack the queen.
A potential attacker targeting him or his family has to deal with that fact. This is not a huge problem if you are a random bandit in the desert who can kill him and get away. But if you are going after his home than it most certainly is. Because you know that the conditions of such an attack on such an important persons home so close to the queens own capital by necessity means that the queen will retaliate with overwhelming force in revenge. Not just because she likes him, even though she clearly does. But because anything less would undermine her authority and position as a monarch.
If she that can't even protect, or at least avenge, her closest and most vital servants when their home is attacked literally a stones throw from the capital city than she has shown her self to be impotent and weak. And impotent, weak monarchs quickly lose the trust of their people and nobility and tend to not last long. So she simply cannot be seen doing anything less.
So if the MC's house were to be attacked than she would have no choice but to retaliate as if her own palace had been besieged. And potential attackers know this. So from that perspective the MC does not need guards around his house because the threat of the queen alone might as well be a force field.
This sort of arrangement was pretty much the norm throughout premodern societies.