I have very little knowledge on this topic but generally speaking I believe it would be possible. People have managed to hang themselves with scarves or elastic bands.
Of course the belt thickness as well as the doorknob sturdiness must be appropriate. You can find resources about your method with the search function.
Welcome to the community and please, allow me to give just a tip of advice: don't rush things.
Take time to make up your mind and, if you're absolutely sure about your decision, just take time to plan things carefully. All the best whatever you decide to do