Connecting two Dell monitors to 2018 Intel MacBook Pro

MacBook Pro (13-inch, 2018, Four Thunderbolt 3 ports) - Technical Specifications - Apple Support

That Mac supports using two external 4K displays at the same time as the built-in screen.

I suspect that the combinations of adapters you tried either are invalid, or simply don’t work due to limitations of the adapters. Get a USB-C to DP adapter or adapter cable to use with the second display’s DP input, and you will only be doing one, straightforward conversion, and may have more luck.

Do not connect both monitors through a single dock or hub unless it is a Thunderbolt dock or hub, not just a plain USB-C one.

Re: “I tried using a DP to HDMI cable and connected it to a USB-C adaptor “

Since you said that the second monitor had DP, but not HDMI, this sounds like you tried to feed the output of a USB-C (DP) to HDMI adapter into a DP to HDMI adapter that you were using in reverse. No need for the trip from USB-C (DP) to HDMI, plus the second adapter was probably unidirectional in the DP (computer) to HDMI (monitor) direction, and so had no chance of working when used in reverse.

Re: “Macs do not support DisplayPort MST daisy-chaining, so that will not work even on Macs that support multiple external monitors”

Also, if the first monitor was being fed a HDMi signal, there would be no DP out signal available for DisplayPort MST daisy-chaining even if you were using the monitor with a Windows PC.

Macs do not support DisplayPort MST daisy-chaining, so that will not work even on Macs that support multiple external monitors.