MacBook Pro takes a long time to sync to external monitor

Your 4K display appears to have

Connectivity

Interfaces

• HDMI
• DisplayPort 1.2
• Audio line-out

using a USB-C to DisplayPort cable will work MUCH better.

if you buy one, try to limit length to one meter.

<< I have the monitor attached to 2 sources (work and home laptop) and an HDMI switch box that I use to flip between the 2 input sources. >>

you should have LED with that, as it changes the direction of the discussion.

The Mac does not rely on windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

if the display does not respond (because the switch is in the other position) no data AT ALL will be sent to the display.

so sorry, that message was edited wrong

it should read, Apple recommends NOT using a converter to obtain HDMI

Apple recommends using a converter to obtain HDMI.

If you must use HDMI, connect directly to the built-in HDMI port with a certified "Premium" or "ULTRA " HDMI cable.

if you need more help, please include the model-year of your MacBook Pro and what processor {plain, PRO, MAX} would be helpful. along with the EXACT model Dell display, or a link to its specs.