Is a 240 Hz monitor worthwhile for me?

I mainly play Fortnite there so have 200 to 240 fps (more 240 fps). Sometimes the fps go down to 190 but only for a short time. If 15-20 people are still living in the end, I also have 190 to 230 fps, sometimes very briefly 150-170. Is a 240 Hz monitor worth it at these fps?

It has nothing to do with it and "no" is my answer.

If you are a professional e-athlete, definitely!

Otherwise, actually less, but more fluid is always possible xD
You can do that, maybe you will meet a few opponents earlier

I mean that it is not worth it for 1 game alone.

Better a higher resolution at 120Hz

I strongly assume that you currently have a 144hz monitor. That is really enough, unless you want to put a lot of money into a 240 Hz monitor… So I say no!

144 Hz are completely sufficient.