How to connect 4 external monitors to operate independently from 2019 MacBook Pro

I’d suggest the OWC mini-TB3 which drives a pair of HDMI displays in extended mode.

https://eshop.macsales.com/shop/docks/owc-thunderbolt-3-mini-dock

You could use two of them leaving you two open ports on your Mac, or one of those and the Apple USB-C DV adapter.

https://www.apple.com/shop/product/MUF82AM/A/usb-c-digital-av-multiport-adapter

You connect your 96 W adapter to that and it powers your Mac and gives you one HDMI out, and that plus the mini-TB3 dock and a USB-C to HDMI leaves you one free port.

Last option would be to just power the cooling pad with a USB-C wall-wart power supply, get three USB-C to HDMI adapters/cables and the Apple adapter linked above.

First, you need to have a 15” or 16” MacBook Pro. If your Mac is a 13” model, it only supports two external displays as independent desktops.

Assuming you have a 15”/16”, there are a few options. If you have Thunderbolt 3 displays, you can daisy chain a pair of them if they support it. Since you’re using HDMI, I assume you don’t have TB3 displays.

So, you’ll need two proper docks that support dual displays. Like the other <$100 docks/hubs found on Amazon, it only supports one display from a Mac, and if you connect two they are mirrored. This is from Anker’s website:

Docks that actually support dual displays are from Brydge (Stone Pro), Elgato, OWC, Belkin and Kensington, and they are $200+. (Personally, I use a Stone Pro at home and an Elgato at work), You’ll need two of them to drive your four displays. You’ll also likely need adapters from the USB-C / DisplayPort outputs of the docks to HDMI, although if your displays have DisplayPort inputs that’s better.

You’re welcome!