Kubuntu 24.04 LTS startup.and general maintenance

Can you please tell me 1.how to stop the system from stopping me from 
using other programs once I e.g.leave the music player running for a 
long period, E.g say, Clementine for about,1/2hr the whole system 
becomes in operable unless I reboot. This can be quite a nuisance

2.how do I stop k torrent from running every time I boot up the system,

Regards Brian.