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

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.

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

Same issue here on MacBook Pro M2 with an external 4k LG monitor. It was working fine in Ventura. It is not recognized in Sonoma via USb-C. It works via HDMI. However I have two external monitors and need to use USBC for one. apple please fix this ASAP!

That’s not very helpful if you’re like me and have Apple Thunderbolt Display. The Thunderbolt cord is literally attached to the display and you can’t remove or replace it.

Everything worked flawlessly for 3 years, multiple OS updates… until the day I installed Sonoma. Issues ever since.

Same problem here on a MacBook Air M1 2020.

Using a Philips PHL 272PV 27" display.

Using refresh rate 60 or 50 Hz no signal, 30, 25 and 24 Hz no problem.

Same issue here after the upgrade. Macbook Pro 15(Intel)'' -> CalDigit TS3Plus -> Gigabyte MU28. Works fine in 24hz, black screen in >= 60hz.

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 :)

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...

Me too. I Unplugged the mac magsafe power from the macbook. Then I had the USB C/Thunderbolt going straight from the mac to the monitor. I turned the monitor off and on spamming the button a few times and it just started working inexplicably.

same issue with Samsung 34 inch curved monitor. monitor is recognized for a second or two before disconnecting and this repeats. unfortunately monitor has only 50/60Hz options and monitor doesnt work in either settings.

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.

Similar issue here any suggestions?

imac 27” 2020

thunderbolt display

for years they’ve worked flawlessly, after Sonoma upgrade every time my imac goes to sleep overnight and I wake it up the next day - the Thunderbolt Display is not recognized. I restart and everything works.

not ideal. :(

Same here.

My MacBook Pro with

Processor: 2,6 GHz 6-Core Intel Core i7

Graphics: Intel UHD Graphics 630 1536 MB

is unable to connect to the thunderbolt Display after the upgrade to Sonoma (14.0).

I can connect, but after a few seconds the display goes black. I tried restart with Option+Command+P+R key until 2 times restart sound (resetting NVRAM/PRAM), unplugging the power from the display and waiting 10 seconds. Nothing works.

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.