I have an external monitor with only USB-C as input (Lenovo M14), and i have an old laptop (Lenovo 2017) with only HDMI and Min Display port as output.
I seek for an adapter in internet but and i dont found, any idea ?
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"i want use it with an another laptop, and i don't understand why they isn't found an adapter :)"
Full-featured USB-C port usually does have the capability to switch into Displayport mode, but the DisplayPort cannot turn itself into ALT-DP Type-C mode. That's why you can see a lot of dongles that connect Type-C port to DP cable (direction from Type-C-host to DP-monitor), and not the other way around.
While it is technically possible to bridge the DP output to Type-C cable electrically, you need to negotiate the ALT-DP mode with your monitor. To do so the driving port must have special Power Delivery messaging capability. The DP alone does not have this capability, so there must be an intelligent controller to drive the Type-C receptacle port and make the monitor to think that it is connected to a real full-featured USB-C port with DP support. This old thread illustrates the challenge to make it happen. See also this youtube video. It looks like the DELOCK 63928 device is only the one in the market to implement this idea. However, you might need an external Type-C AC-DC adapter to provide the power to your monitor; the DP will unlikely to supply it.