How to save underscan setting

I'm here searching for an answer to this as well. I want Apple to release a Sonoma update that saves the underscan setting.

I can tell you this bug has existing over several major releases now and Apple just doesn’t seem to want to fix it despite multiple tickets to them over the years. For the record, this problem still exists on a Mac Mini 2023 running Sonoma 14.3.1.

I just started using a Macbook Pro M3 a few weeks ago and have the same set up (using flat screen TV for 2nd Monitor) and problem - ie. I have to reset the underscan every time I wake up the laptop. In other words the laptop is in sleep mode and when I wake it up I have to reset the underscan. Very frustrating indeed. It would be great if an Apple tech would weigh in on this problem.

Apple Support had no answer. I am using a brand new (1 week) MacBook Air and an older Toshiba televison attached with an HDMI cable to a HDMI, USB and USB-C adapter. The same setup worked fine on my 1995 MacBook Air. Apple Support told me to try using a HDMI cable directly to the MacBook or get a new monitor. I really don't think the cable suggestion would work and I really don't want to invest any more money.

Any suggestions?

I wouldn't do either of those things. If it worked before clearly software is able to handle this, they just ditched the feature and of course need to tell you how everything OTHER than them fixing it will solve the problem.

did you ever find out how? this is so frustrating

Then I suggest you contact Apple support. Start with the "Support" link this page lower left.

Are you using an app for this or native Mac functionality?