Can I ask my supervisor to let me graduate early?
Early graduation is often (usually?) possible, but only if you were quicker than other students with the necessary work, not as a way out if you don't like the program.


  Is it advisable to talk to my supervisor directly about early graduation? I would tell him that I am not happy with the research and I want to write a thesis on a closely related but less intriguing subject and just finish my master’s as soon as possible.


I expect that this line of argumentation to have a very small chance of success. If your main argument to early graduation is that you hate the program and want to get out, they will likely suggest you to drop out. If you want to have any chance at early graduation, find out where the bar is (in terms of required research output and coursework) and work hard to fulfill it as soon as possible. Then discuss with your advisor that you wish to graduate as you have done the required work (not because you dislike the work).

Stay far away from any argument that you hope they will lower the bar for you because you do not enjoy working with them. This will not have the anticipated effect: instead it has a good chance of antagonizing your advisor, in that way lowering your chance of early graduation. And you will need their goodwill to graduate early and (realistically also to  graduate at all).