Click once on the dotted area above to activate.
Keep this page open to prevent your desktop from sleeping.
Safari is recommended on Mac for lower power consumption.
The tab must be focused, or right-click>Enter Picture in Picture ..
.. on the new MacOS you can drag over to the right to fold it.
In cases your system has a sleep policy you can't control and you need to get around that.
On Safari it consumes about ~150Mb, almost no CPU / GPU.
I've noticed that when a video was playing the OS wouldn't go into sleep.
So instead of having a Youtube video playing I've created a short ..
.. 8x8px video, mostly just a white square with minimal sound..
.. and uses JS to keep playing.