if I am on instagram or titter as a digital artist and people commission me to make a landscape and pay me. Is it haram to do that since they may be using my painting for haram things
You have only a limited responsability for what happens with your paintings.
- It is haram if your paintings incite to do haram things.
- It is makruh if you know that your customer is often using them for haram things.
If there is nothing wrong with your paintings by themselves and you sell them anonymously or to anyone of whom you do not know an evil purpose - which is probably the case with your work -, you are not responsible for what is done with it later.