Macbook pro having trouble detecting two matching monitors

Here's a possible solution I would not have thought of.

https://www.reddit.com/r/MacOS/comments/wes38j/identical_monitors_pushing_same_edid_and_display/

"To close the loop on this, I just bought a $20 EDID Emulator with HDMI pass-through fro Amazon, and this solved the problem. It now sees one monitor identified by the pass-through as a Dell instead of an LG and therefore lets the Display arrangement stick"

There seem to be lots of these on Amazon. I'm surprised by how many there are. I'm not sure if all support 4K resolution at 60 Hz, so check descriptions carefully – but many supposedly do.

https://www.amazon.com/s?k=edid+emulator+4k

JuanDBB wrote:

With two usbc to hdmi cables.

That rules out the possibilities that you're trying to daisy-chain the monitors (not supported) or to connect two monitors via a non-Thunderbolt dock (also not supported).

They are two 4k monitors. I'm getting used to unswitch/switch the two usbc every morning, as otherwise it only detects one of the monitors.... but it would be great to work normally... I have read elsewhere thta the problem is that the monitors are exactly the same model and the macbookpro get confused...

I think the problem to which you are referring is not just that the monitors are exactly the same model. It is that they are supposed to have unique electronic serial numbers in their EDIDs (Extended Display IDs?), just like all Ethernet and Wi-Fi interfaces are supposed to have unique MAC addresses.

Some manufacturers reportedly take shortcuts when loading firmware for monitors. They load entire batches of monitors with exactly the same image – including the exact same electronic serial number in the EDID. If you are unlucky enough to get two monitors from the same batch, and your computer was counting on serial numbers to actually be useful for telling monitors apart, that's when things go sideways.

That Mac should have no trouble driving two external displays.

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MacBook Pro (15-inch, 2019) - Technical Specifications - Apple Support

Simultaneously supports full native resolution on the built-in display at millions of colors and:

• Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors
• Up to four displays with 4096-by-2304 resolution at 60Hz at over a billion colors

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How are you attaching the displays?

What I don't know is how you set up these "EDID emulators" – since ideally, you would want it to report back the same EDID information that's in your monitor now, just with a different (unique) serial number.

Which specific MacBook Pro model do you have?