Hi there @guga2112, welcome! Actually Aseprite never supported moving with the arrow keys the current cel when the Move tool is active. There are plans to implement this in a near future (along with other options).
Anyway you might be confused with the selection tool, you can use the Rectangular Marquee (M key), then select the whole canvas (Ctrl+A) and then the arrow keys can move the selection content. I hope it helps!