Are there disadvantages with the curved monitor?

I wanted to get a new monitor with WQHD 144 HZ.

I saw one who also had curved.

If I buy it now, will my aim be worse in games like Fortnite?

Because I've never played with such a curved.

No, many see this as an advantage even after a short period of getting used to it

Curved may be unusual, but may reduce distortion. But that depends on monitor size and monitor eye distance.
I can only recommend it, especially with Ultra Wide (which I can also recommend).

No. If you can connect 2 monitors, you can connect 1 curved monitor and 1 normal monitor. I also did it at the beginning because I mostly work with 2 monitors. Now I have 2 curved monitors.