Flickering screen, not adjusting brightness

[jo3p]

First of all, I'd like to thank you for all the effort you've put in to this program and the support you still give!

I'm having a hard time getting the app to function properly.
Hardware used:
MacBook Pro 15" 2016
MX Keys keyboard. Seems to respond to the F1 and F2 keys. :)
Two Philips 243V external monitors.
One of the monitors is connected with a USB-C to HDMI-cable. The other one with an old Microsoft XBOX HDMI cable and an AliExpress USB-C dongle (replica to this one).

I do remember getting some external-brightness-adjustment-app to work properly with a BenQ monitor I once owned, not sure if it was the same app.

Anyways, when I try to adjust the brightness on the external displays, they just turn black for a second, and the brightness is not adjusted. Could this problem be on the side of the displays?

Thanks in advance!

Joep