How to fix refresh rate Issues on Dell monitors after Sonoma update

I have just 'downgraded' my OS back to Ventura and everything works normally now. Ngl, I think I spent too much time troubleshooting this issue and even Apple Store Techs are not aware of it. I will soon contact the online support and get a Tier 2 Data Capture and see what actually happened.

To get OS Ventura back, you have to back up everything using Time Machine.

Erase your mac.

Restore your mac to its original OS (Say mine is Macbook 2019, so it will get back to Catalina)

Download Ventura on App Store.

Install it Ventura, restore all your files.

Violà :)

I just fixed this issue. The solution was to purchase a new USB-C 3.2 cable that supports 40 Gbps and 240 W of charge.

My experience:

July 2023: Purchased a certified USB-C 3.1 cable that supports 10 Gbps and 100 W of charge. It connects beautifully to my external monitor.

Early Oct 2023: Get a laptop with Sonoma. It does not connect to my external monitor. I follow all the advice on this thread, and nothing works. I purchased the above new USB-C cable, and it connects flawlessly.

Note: Be very careful to get a USB-C cable certified for 40 Gpbs of data and at least 100W of charge. I had to purchase multiple USB-C cables before it would work (I'm currently returning them).

Yet another reason why I loath OS updates.

From Greatlorens at the top of this feed:

"Can you try resetting the Dell's monitor settings to the factory ones? and then open the monitor setting and check that DDC/DI is OFF, LCD conditioning is set to off, HDR to off, and USB C prioritization to "high-speed setting" These settings demand less power from the monitor. Then check in Mac screen settings in "advance" section if the Show resolutions as list is toggled on. that's the basic I can tell. If Sonoma breaks something else I don't know. I do have a Dell 4k but I have an m2 Mac without these issues you mentioned. maybe it has something to do with m1? but it's a bit strange."

Just wanted to say thank you and that this total fixed the issue I was having. Running a Mac Studio on M1 Max with two DELL 32" monitors. One via HDMI and the other via USB-C. The USB-C was not waking / activating when coming out of sleep mode on the computer. I'd have to turn the monitor off then on again to get the Mac Studio to recognize it. This all happened after updating to Sonoma for the first time. Your suggestions (pasted above on my message) fixed it, so thank you!

Cheers.

UPDATE. I backed up my MB Pro with Time Machine, created a bootable disc with Ventura on it, erased my internal MB hard drive, reinstalled Ventura with the bootable disc and now my Thunderbolt monitors work flawlessly again. Sonoma is definitely the culprit. Get yo stuff together Apple. Sheesh. Pry this Ventura from my cold dead hands until they acknowledge they've fixed monitor support issues...

ok a monitor full power cycle off and turning it back on has resolved the issue. so random, but glad its working.

Had the same issue with my LG monitor.

Unplugging my monitor for 10+ seconds from the wall socket did the trick.

Can you try resetting the Dell's monitor settings to the factory ones? and then open the monitor setting and check that DDC/DI is OFF, LCD conditioning is set to off, HDR to off, and USB C prioritization to "high-speed setting" These settings demand less power from the monitor. Then check in Mac screen settings in "advance" section if the Show resolutions as list is toggled on. that's the basic I can tell. If Sonoma breaks something else I don't know. I do have a Dell 4k but I have an m2 Mac without these issues you mentioned. maybe it has something to do with m1? but it's a bit strange.

On my MBP/M2 I had to shutdown the MBP (not restart) (apple menu/shutdown). I waited 30s to make sure it was shutdown then powered on from the power button. Since then the external display is recognized via thunderbolt/USB-C cable, which also charges the MBP. It is recognized even after I put it to sleep.

Same issue, I cycled the power on the monitors (hard cycle, by pulling the power cord) while still connected to the usb c/thunderbolt port. When the monitors came online I received a prompt from the Mac book to connect external displays.

For what it's worth:

I too had this problem but just got mine resolved. I used a good quality usb c to HDMI adapter plugged in to the port right next to the mag safe adapter, and got a newer better HDMI splitter (5 in 1 out) with a bigger power supply than I previously had, and set my monitor to use HDMI 1.4

I found I could connect a DELL monitor, but when I changed (Unplugged and went to Viewsonic) that to my second monitor via a USB hub I could not connect. If I used a direct USBC to HDMI adaptor ( ( Vention 4k 60 Hz). it works.

It worked after I shutdown my MBP and then powered on again. Just unplugging the external monitor did not work.

I had the external display flickering problem on my M1 Air since I upgraded to Sonoma.

I cleared nvram: sudo nvram -c

I pulled all of the devices connected to my LG 24" Ultrafine and had less problems.

It acts like a Thunderbolt port is bad on the display so I switched to the other one.

The affected tbolt port on the display I know is fine.

M1 Pro that's still on Ventura runs the display completely fine with devices fully populated to the LG's internal hub on either tbolt port.

I tried just about everything on this thread and nothing got my Dell P2719HC monitor to be detected by my macBook Pro immediately after upgrading to Sonoma 14.1.1. My monitor indicated "no USB-C signal detected" and the MBP did not recognize the monitor at all. I did read on another site that switching the USB-C cable end to end was something to try. I thought that was silly and could not figure out what that could possibly do to effect the problem but I did that and it fixed the issue immediately for me.

Same issue here with an external 4K Samsung monitor.

My Mac mini (M2, 2023) started recognizing my display again only after downgrading the OS to Ventura from Sonoma.

I strongly recommend downgrading the OS if anyone is facing the same problem.

Mac mini with Sonoma did not recognize my display no matter what I used (HDMI & DisplayPort via USB-C).