HDMI screens have blanking support, DSI screens not. DSI screens can however turn off the backlight with: echo 1 | sudo tee /sys/class/backlight/*/bl_power and on with echo 0 | sudo tee /sys/class/backlight/*/bl_power to have this happen without requiring a password ls /sys/class/backlight/ to get the name as panel_backlight@1 then sudo visudo -f /etc/sudoers.d/backlight-blank and add

<username> ALL=(root) NOPASSWD: /usr/bin/tee /sys/class/backlight/panel_backlight@1/bl_power

To have this done automatically edit ~/.config/labwc/autostart

swayidle -w timeout 600 'echo 1 | sudo tee /sys/class/backlight/panel_backlight@1/bl_power' resume 'echo 0 | sudo tee /sys/class/backlight/panel_backlight@1/bl_power' &

Now reboot the system