After Monterey Upgrade, Strange HDMI Connection to my Dell U3420Q

Your specific model, 2017 MacBook Pro 15-in, does not use MagSafe. So the most obvious choice to consider is the USB-C cable and take advantage of the display's willingness to supply power when the MacBook Pro wants to accept operating power. Your Mac will never use that power to charge its battery unless necessary, and will NEVER over-charge.

Be sure that any USB-C cables for displays are certified, under ONE meter in length, and have at least this logo or better:

...

Your display appears to be "4K" display with:

2 x DP 1.4 (HDCP 2.2),

2 x HDMI 2.0,

1 x USB Type-C (Alternate Mode with DisplayPort 1.4, USB 3.1 Upstream Port, Power Delivery up to 90W)

The BIG Surprise is that the data rates for a Hi-color "4K" displays like yours are higher and more incessant that ANY other connection to your computer, including the connection to the Drive(s).

A 10 bits/color connection to your 4K display using HDMI consumes 14.4 G bits/sec, faster than USB-C 3.1 10 G bits/sec port, and uses up about three quarters of the bandwidth on a USB-C 3.2 20 G bits/sec port like those on your Intel MacBook Pro. (This also suggest any Drives you have connected on the same Dock will be slowed by the display data.)

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HDMI was invented for 720P TV sets, and is generally NOT up to the task, it can sometimes be stretched to get close to appropriate performance, but it really shows its age if and when you can get it to work.

So my first recommendation is to re-think your connection and back away from using HDMI -- AT ALL -- for this high-end display.