LG Ultrafine 4K display + 2021 16-inch MacBook Pro?

I've purchased two LG Ultrafine 4K monitors, one at home, and the other at the office, to couple with my MacBook Pros, first an 2017 MacBook Pro 15", and then a 2021 MacBook Pro 16" M1 Pro. It's been about a little over one month of use without problems with my 2021 M1 Pro MacBook, but in the past few days, something went wrong. When I plug in the USB-C cable connecting the Ultrafine 4K into my 16" M1 Pro MacBook, the monitor flashed on and off, and so was the charging sound. But there was no problem with the 2017 MacBook Pro 15.4". My guess is the power output was insufficient to power the 16" M1 Pro, because when I connect the laptop with the 140W MegSafe, and then the Ultrafine 4K USB-C, then the screen can be output to the external monitor. It's a pity though that the original intention was to simplify the connection with only one USB-C cable but it doesn't work well problem-free with the new 2021 M1 Pro 16" laptop.

Apple does not recommend using a Power adapter smaller than the one intended to "regular" charge your Mac. They are unlikely to add their blessing to anything less.

My recommendation has always been that if you MUST use a lower capacity power adapter, you use it only for emergency re-charging, and only when the Mac is nominally off, so as to avoid under-powering while running.

what Soosie_1215 said, plus this as well:

Use a USB-C charge cable

You can use any of the Thunderbolt 4 (USB-C) ports to charge your Mac with a USB-C charge cable. Your Mac charges over only one port at a time, so connecting multiple power adapters to the MagSafe 3 port and Thunderbolt 4 (USB-C) ports won't result in faster charging. If you connect more than one power source, your Mac charges only from the adapter providing the most power.

--from:

Charge your 14-inch or 16-inch MacBook Pro - Apple Support

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Hi there Laurence Cable,

Welcome to Apple Support Communities. We see you have some questions about using a third-party external monitor with the new MacBook Pro, along with questions about power. We'll do our best to provide some guidance. If you are referring to this particular LG monitor (aka "original"), then it should work.

24 Inch UltraFine 4K UHD IPS Monitor with macOS Compatibility

See the guide here:

Use the 23.7-inch LG UltraFine 4K Display with your Mac or iPad

"The LG UltraFine 4K Display requires a Mac with a USB-C port or Thunderbolt 3 (USB-C) port running macOS Mojave 10.14.5 or later, or an iPad Pro or iPad Air with a USB-C port."

That will include the new MacBook Pro 16-inch with M1 chip. As for the question about it being able to power the new MacBook Pro, the quick answer is: No, because it is providing less power than needed. Read more here:

Find the right power adaptor and cable for your Mac notebook

"If you use a power adaptor that is lower in wattage than the adaptor that came with your Mac, it won't provide enough power to your computer."

All the best.