Monitors won’t sleep on idle pc

So I’ve set up pop os, everything went smoothly. But I have a problem - My pc is set to turn screens off after 15 mins, also to lock itself. But when it does that, my monitors shut down for a second, then start again so I can see it’s locked, then after few seconds monitors are blank but not turned off, led indicator is active and so is backlight panel.

It bothers me because I don’t want to physically turn off my monitors every time I go afk.

Can anyone tell me where to set this up? Thx