Put display to sleep while using one external screen?

[resting]

I've connected iMac to an external screen, which is larger.

Is there any way to put the iMac's screen to sleep while I'm watching movies fullscreen on the external screen?

Right now it's just too distracting even with the brightness turned all the way down.

I'm using them as separate spaces cause sometimes I do want to watch movie on one, while checking out some stuffs on the other.

There's gotta be a way to put it to sleep when its not needed tho right?

 

[bogdanw]

There is an app https://github.com/Eun/DisableMonitor, but it’s no longer maintained and comes with this note:

Warning
It has been reported that the software is able to cause irretrievable damages to your computer.
Use at your own risk!

 

[resting]

There is an app https://github.com/Eun/DisableMonitor, but it’s no longer maintained and comes with this note:

ah, thats risky. I realise Hazeover can dim the other display.
Am using Hazeover for now since I already had it

 

[bogdanw]

There is an updated fork, tested on Big Sur https://github.com/epalzeolithe/DisableMonitor-3.0