In KDE you can click on the Display Configuration icon in the system tray & select “Enable Presentaion Mode” to stop your system from suspending.
Alternatively, you can use systemd-inhibit to launch any application for which you want to keep the system running, eg: systemd-inhibit minitube.
systemd-inhibit defaults to inhibiting “idle:sleep:shutdown” if no options are included in the command. You can view all the options at: systemd-inhibit — Execute a program with an inhibition lock taken