Revised Answer:
After taking a closer look at USB-C or Thunderbolt 3 and how they achieve video output, I don't think an adapter exists to connect an HDMI video source to connect to a USB-C display. Even the official HDMI website shows the conversion as being one-way: USB-C to HDMI.
A major caveat is that sending HDMI over USB-C requires the video source to send additional signals that are not part of the HDMI specification; They're part of the USB-C specification.
For conversion in this direction to work, an adapter would have to be a USB-C Host controller and signal to the monitor that it wants to use the HDMI alternate mode. Creating a video adapter that acts as a USB-C host device is not trivial, and almost pointless since most devices or screens have multiple video connectors to use instead.
I believe that it may be possible to make such an adapter, but the demand for it is too low for any to exist yet.
Old Answer:
"This is 2019." Yes, but new video connectors don't always make things simpler.
To answer your question seriously, the thunderbolt 3 (USB-C) connection uses a DisplayPort signal for video. Unfortunately HDMI to DisplayPort (in that direction) is not compatible with just a simple wire-to-wire converter. You actually need something known as an "Active HDMI to Displayport Adapter", and obviously the displayport side needs to be the USB-C connector.
I am also fairly certain that the USB-C monitors get their power from the USB-C connection. If you have a monitor like that, the adapter would have to supply power too!
I have never seen an adapter that meets all of those requirements so I cannot recommend one for you.
It might be possible to combine two adapters:
- HDMI -> DisplayPort
This one must be active, so requires its own power usually from USB.
- DisplayPort -> USB-C
This one may be VERY hard to find in this direction but theoretically possible. (It probably doesn't exist.)
Old Update:
It turns out that I entirely missed that USB-C (and thunderbolt 3) can output HDMI signals too (as an Alternate Mode on top of USB-C). That implies that USB-C displays (but not necessarily ones that require Thunderbolt 3) can accept HDMI signals through that connector. This raises some hope that there is a passive HDMI to USB-C cable/adapter out there. (This isn't possible without negotiating the video mode over USB first.)