MacBook 16-inch Battery Life Issues

Yep I figured as much. The problem with Apple Support is they may know more about the hardware but when it comes to software it's a hit or miss unless they are running the same softwares. Also since the MacBook Pro 15"/16" is the only Mac with graphics switching it may explain why they didn't know. Every other MacBook has Intel Integrated only and the iMacs and Mac Pro have only a dGPU.

Spotify is your issue 100%. I honestly have no idea why Spotify needs the dGPU but it definitely activates it and drains battery.

Here's my list of known softwares that activate the dGPU:

Apple's Photos app.

Spotify

Chrome

Pixelmator

Final Cut Pro X

Logic Pro X

Adobe CS/CC

There are more but I don't know off the top of my head. Apple's Music app and iTunes and Safari do not activate the dGPU.

Because of complaints about the issue, Apple did additional engineering work on the 13-in model, and made additional recommendations summarized in the article cited below.

Your Mac will Never over-charge. Be certain you have done a process similar to the process in that article, and whenever possible, connect your power adapter.

If your MacBook Pro (13-inch, 2019, Two Thunderbolt 3 ports) keeps shutting down - Apple Support

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The article is not for your Mac, but it was cited because its suggestions may be applicable anyway.

Some battery longevity problems are related to the Mac detecting the proper "full point". User hesitation to connect the power adapter for a long period of time and allow the MacBook Pro (all models) to charge deeply is likely to be related.

It appears that when you do allow it to charge deeply, it self-adjusts the "full point" over time, and improves battery life overall.

What app are you using for music? Also always check to see if your dGPU is activated because it sounds like it is. Certain apps will activate the dGPU without the user knowing. This will deplete battery much faster and even cause the machine to heat up because more energy is being used. To check to go the Apple Menu-About this Mac and verify if both the Intel Integrated Graphics and the AMD Radeon 5000 series GPU is listed. If both are listed then that's your problem. Obviously one of your apps are causing this. Normal apps that only need the Intel Integrated Graphics won't activate the dGPU and it won't be listed in About this Mac.

Sorry I forgot to answer your question about switching. You can only switch to the dGPU only. You can't choose to use the Intel Integrated Graphics unless you use a specific program that does this. By switching from the default dGPU to Intel Integrated Graphics on softwares that use the dGPU will cause slight jittering when scrolling and perhaps more unstable operation.

In System Preferences choose Energy Saver. You will see a check box for the Graphics Switching. If you uncheck it the dGPU will remain on no matter what app you are running. You don't want to do this.

Quit all your apps and you'll see the AMD GPU no longer listed in About this Mac. When you launch apps check it, this way you'll know what apps are draining your battery.

DPJ wrote:

Also since the MacBook Pro 15"/16" is the only Mac with graphics switching

I think you left out the word "Current" MacBook Pro in that statement. This dual-graphics processor "trick" has been implemented since the 2008 15-in MacBook Pro.

True. I guess my point was most Macs of the entire line have either dGPU's only or Integrated GPU's only. Under that situation it's understandable that Apple Support may not know which softwares cause Macs with graphics switching to "switch", therefore putting the customer through unnecessary troubleshooting steps as they did with the OP.