MacBook Pro M4 Pro Not Recognizing External Monitor via Thunderbolt (Worked on M1 MacBook Pro)

I'm in a similar position, not identical but I think the root cause is the same...a setup that used to work perfectly with my M1 Pro MacBook Pro doesn't work with my M4 Pro MacBook Pro. I use 2 external displays at my desk, a Dell 40" Ultrawide 5120 x 2160, and a standard Dell Ultrasharp 24" 1080p.

They both work fine individually, and allow me to select the full range of expected scaling options. However when I connect both together, a few scaling options disappear from the resolution list of the 40" display (unfortunately, my preferred HiDPI resolution among them—3840 x 1620).

Appreciate the problem is different, so this isn't very helpful...but the shared experience being that, this is something that still works just fine with my old M1 Pro MacBook Pro—even if I plug it in and test right now! Very frustrating that this one issue is forcing me to change how I work, on a device which in most other ways is so superior to the M1 Pro version.

I was hoping it would be resolve in an update but months later nothing has changed...

These are subtle issues. I do not have a good idea of exactly what these problems might be.

So these are "just some ideas"-- not a standard checklist.

Does your 90 cm cable have the Thunderbolt trademark on the end that plugs into the computer? Was it sold as an ACTIVE cable/adapter?

What we think of as "normal" cable/adapters cables are USB-C cables and passive -- they rely on DisplayPort Alt Mode. This means the computer generates DisplayPort signals DIRECTLY, and packs them inside a USB-C envelope, and the adapter passes the signals along untouched. These are all limited to one meter or less.

There can also be more expensive cables sold as ACTIVE cables. These contain electronics that take the DisplayPort signals provided by the computer, unpack from ThunderBolt of USB-C envelope, repacks then into a DisplayPort envelope, Re-drives the signals with electronics in the cable/adapter, and sends them to the DisplayPort device. If they have a genuine ThunderBolt interface on the computer side, these could be running into obscure issues when interfaced to Thunderbolt-4, which has never seen before in the wild.

In theory, ACTIVE cables might be able to be slightly longer before developing issues due to cable signal deterioration losses.

another possibility: If the cable "pretends" to be a Thunderbolt cable, Thunderbolt signaling is TWICE the speed of USB signaling. This might overwhelm certain adapters, or possibly certain displays.

I have a innocn OLED monitor works great when connected with any cable to a Windows box but,

Both the M1 Mac Air and the M4 Mac Mini I have simply will not display any signal

the screen will cast to the external monitor as the screen on the Air will default to the extended mode

but the screen shows nothing but Blank

had several calls to Apple support with no pertinent info regarding the issue

I am not alone with this issue and Apple Support now acknowledges this is a Known Issue.

<< using a USB-C to DisplayPort cable. >>

how long is that cable? {one meter or less, Longer}

EXACTLY what model display?

What worked for you? Did you use a different cable that resolved your issue?