iMac stuck on max brightness in Target Display Mode

[WillNilges]

Is there any way to adjust the brightness of the display while in target display mode? It's so bright it's almost unusable!

[mwkchan]

I have the same issue. I think somehow need to find an SMC value to adjust the brightness

[zft9xgy]

Just adding some context: im using a macbook air m2 ventura 13.4.1 and display an imac mid-2009 with Ubuntu.
smc_util script works for me but there is no way to modify bright, so this app solve my problem.

This solve my problem out of the box -> https://github.com/waydabber/BetterDisplay