I chose the light, latest Raspbian, without the desktop environment, or X Window (X11).
As of June 2024, even if the Raspberry PI imager does have the configuration options for headless access (ssh enabled and creation of a user) after first boot, they don't work for Raspbian.
You have to mount the fresh SD card back on your computer and add two files:
an empty text file named "ssh" and another text file named "userconf.txt" with the line username:password for the default user, that will be able to ssh in and have sudo access.
Follow the installation instructions that you can find on the HamClock creator's website: https://www.clearskyinstitute.com/ham/HamClock/ , on the "Desktop" tab.
As Elwood WB0OEW, the author of HamClock, kindly wrote in an email, HamClock does not require X Window to run, as I previously mistakenly stated.
Check the FAQ 14 on the HamClock's website
The installation script will ask:
build for web access only (no hardware display)
The resolution is relevant, even if you'll be using HamClock with a web browser.
You can now run HamClock headless and access it via a web browser
just run HamClock & and use the following default URLs
http://<your ip address>:8081/live.html - read/write access
http://<your ip address>:8082/live.html - read-only access