Max resolution for external display on a 2019 15" MacBook Pro

Nope. Looks like everyone is wrong here.

https://support.apple.com/kb/SP794

Video 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

Thunderbolt 3 digital video output

• Native DisplayPort output over USB‑C
• VGA, HDMI, DVI, and Thunderbolt 2 output supported using adapters (sold separately)

OP, have you tried holding Option on the keyboard then clicking the "Scaled" button under displays?

http://pd.omg.lol/YBC1Oy

The Internet is your friend: a simple search turned this up:

Graphics and Video Support

• Intel Iris Graphics 6100
• Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on up to two external displays, both at millions of colors.
• Thunderbolt digital video output
  • Native Mini DisplayPort output
  • DVI, VGA, dual-link DVI, and HDMI output supported using Mini DisplayPort adapters (sold separately)
• HDMI video output
  • Support for 1080p resolution at up to 60Hz
  • Support for 3840-by-2160 resolution at 30Hz
  • Support for 4096-by-2160 resolution at 24Hz

Coming back around to the Technical issues at hand:

The specs for that MacBook Pro 16-in say that the requested resolution, 3840 by 2160 can be output by the computer.

But they are at best ambiguous about whether the resolutions cited are available over HDMI. That computer has no built-in HDMI ports, so you would need to use an adapter. And now the devil is in the details.

Given that HDMI was originally designed for HD TV at 1920 by 1080p, use at higher resolutions requires a stretch, in this case to at least to a more recently issued version such as HDMI 2.0.

The Apple USB-C MultiPort adapter has a new version available, model A12119. so if you get exactly the correct adapter, you may be successful:

Use the HDMI port of this adapter with a display, TV, or projector that connects using an HDMI cable. It's HDCP compliant and supports the specifications below, depending on the model of the adapter. 

The model number is printed on the retail box and the side of the adapter, near the ports.

Model A2119 is the newest model of this adapter. It supports HDMI 2.0 at these resolutions and refresh rates when used with macOS Mojave 10.14.6 or later or iOS 12.4 or later. It also supports HDR video in HDR10 and Dolby Vision formats when connected to a compatible playback device and display, TV, or projector.

• • • Up to 1080p at 60Hz
    • 3840 x 2160 at 30Hz
    • 3840 x 2160 at 60Hz with these devices:
    • 16-inch MacBook Pro introduced in 2019
    • 15-inch MacBook Pro introduced in 2017 or later
    • Retina iMac introduced in 2017 or later
    • iMac Pro
    • iPad Pro

Model A1621 supports HDMI 1.4b at these resolutions and refresh rates when used with macOS Sierra 10.12 or later or iOS 12 or later:

• • • Up to 1080p at 60Hz
    • 3840 x 2160 at 30Hz

from:

About the Apple USB-C Digital AV Multiport Adapter - Apple Support

Um are you telling people what to do and think again? Are you a mod?

The article I linked to direct from Apple's website states the specs of the 2019 15" macbook pro and they're way different to anything provided in the answers here. If the article has different specs to what users in this thread have stated, then guess what...the users in this thread have posted the wrong information.

Posting misinfo in a forum where people are looking for solutions is detrimental to people's time, and the quality of information that can be found here.

Attacking me for pointing this out?

"Maximum Performance"...my iMac 2015 has had severe screen ghosting issues about a month after purchase. Apple admit it's due to a faulty batch of LG displays used. The exact same display from Apple's DisplayPort family of LG screens which also have the same ghosting issues.

So what is "maximum performance", and why wouldn't a reliable (and much cheaper) screen brand such as Samsung not suffice?

It's not the Brand, it's the Interface.

HDMI displays are not guaranteed have a screen buffer, so the protocol says they send the same information, again and again and again every 60th second as if it were a CRT display. You still need to fetch those characters, rasterize, and send the ENTIRE screen data down the link 60 times a second even when the last frame has not changed. That limits how fast they can change, and limits how many times a second the information can be updated, and generates a lot of heat for nothing.

DisplayPort displays have a screen buffer. When the screen stops changing, the link goes nearly quiet. They run cooler and they can run faster.

Yep that's why I was curious with what you meant by "maximum performance", and you were thinking exactly what I thought you were thinking.

A really obscure answer that has absoltutely nothing to do with what the OP asked.

What is the maximum resolution they can run a screen at, not what the maximum performances of standardized plugs are 🤣

The answer is "3840 x 2160 natively, the Samsung screen is a great choice" 😂

That Mac only supports 3840 x 2160 at 30 Hz over HDMI. Some users get headaches using display refresh rates lower than 60 Hz.

It supports flicker-free displays at even higher resolutions using DisplayPort family, if your display supports that.

I stand by what I wrote above.

philux--

You are welcome to add your observations and experiences to any thread on Apple Support Communities. You are welcome to say that you disagree with what others have said, and explain the reasons why.

You are NOT welcome to tell others they are WRONG, or attack the character of other contributors.

You need to be significantly more considerate of the feelings of others when participating is these discussion.

I am not an Apple employee or a moderator. I have been participating on the Apple forums in its various incarnations for nearly two decades. Unlike many other forums, the Apple forums cultivate civility and getting along.

As someone who has a lot of experience here, I am trying to give you, personally, some tips about how to make this a better place for everyone. Points are awarded by other Users. I did not accumulate my points by disregarding the feelings of others.

If you do not value being civil, there are many other forums where flame wars, insults, and nonsense are tolerated far better than on these forums. Not respecting other people and not conducting yourself better than you have today will get many more of your posts removed.

Since I’m the one being criticized let me just say this: in the early morning after one cup of coffee my eyes saw 15 twice, as in 15” 2015 MBP and that’s what I searched for. So yes, I was wrong. But I was also right...his computer will handle the display he asked about.

in future, it would nice if you’d correct others’ mistakes in a kinder way. We don’t mind being corrected, Grant has corrected me on more than one occasion and I’ve probably done the same for him. But one catches more flies with honey than vinegar as my granther used to say. And if that doesn’t deter you, the moderators here wield a hefty ban hammer.

so the punchline is, ...

... use a DisplayPort family display for maximum performance.