a few months ago i decided to drop windows and start using the kde neon system for my work.

I have noticed that the internet is always going down when I am using kde.
but the problem is only in the system that this happens. because when I'm on windos it doesn't happen and when I'm on cell phones it doesn't happen either. it is only in kde.

someone can help me?

Not sure if this is the issue, & am using Kubuntu 20.04 at the moment. But I had a similar issue there, & had to edit the file - /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf. Wifi-powersave was set to 3. Setting it to 2, saving the file & rebooting solved my problem.
Even if that's not the problem it won't do any harm and is easily reversible.