Basically when you created the server, the software was (1.17 ) like this
The up arrow means it will update the server version to the latest Minecraft version
To disable this just go to Software -> Vanilla -> Choose 1.17 (without the ) or Choose 1.17.1 (without the
) whatever you want. But don't select versions next of it
if you don't want it auto update the Software.
I hope it helps