External monitor can't be detected anymore I know this is a reoccurring issue and I've gone through every forum, every topic and every blog post I could find. Two days ago my MacBook Pro 13 stopped detecting external monitors.
I'm using a Unitek HDMI to USB-C dongle which I know works fine. I've tested 3 different monitors, that have different resolutions and refresh rates, they all work fine.
I've got another 2019 MacBook Pro 13&quot; that works fine with every single monitor; using the same cable/dongle combo.
What I've tried:

plugged the dongle with and without charger also being plugged in,
plugged the dongle when Mac was sleeping/off
plugged in a USB-C -&gt; USB-A dongle and connected a mouse to it - both ports work fine,
restarted my Mac after I've plugged the USB-C cable in,
reset NVRAM and SMC,
reinstalled OS (with and without backup)
tried clicking &quot;Detect Displays&quot; in Displays settings,
closed the lid, plugged the cable in, opened the lid,
installed DisplayLink drivers, uninstalled them.

When I connect the dongle, it's visible as BillBoard Device in the System Information -&gt; USB (both Macs have that). I've also been watching and comparing Console logs when I connect/disconnect the monitor and here are some things that I've noticed:

The Mac that works fine has some [Hot_Plug] events visible when I plug in the monitor,
FB0 both have DisplayPort driver version 1.1, FB1 on working Mac has a version 1.2 (this information doesn't show up on non-working Mac)

The screen doesn't flicker when I connect any external display, there's no Arrangements tab visible. AirPlay works fine.
Both Macs are 2019 13&quot; Pro with the same stuff inside - they both use Intel Iris 645 Graphics.
Any tips?
There's only one thing to do.... take it in for service.

When I connect the dongle it's visible as BillBoard Device in the
System Information -&gt; USB (both Macs have that).

The fact that it's being detected means your port is functioning.  Now, you didn't specifically say so, but I'm assuming that the built-in display is working.  Since you have the Intel Iris (Integrated) graphics, there's no failure with the graphics chipset (there's no discrete GPU)
However, there is a video mux (multiplexer) chip that &quot;sends&quot; video to the LCD, the external monitor, or both.  This has likely died.

Macbook Pro on but display is blank

You've done a lot of diagnostics - actually gone a bit overboard with the re-installation of the OS.  Safe Mode or Recovery Mode is sufficient for this.  For the future, try this first and if you absolutely must have a clean install, do it to a USB flash drive (32GB is sufficient) so you're not wiping out your drive (and all your work) as a diagnostic procedure.