EndeavourOS does only minimal installations. Vulkan is not necessary for Linux or EndeavourOS to run, therefore Vulkan is not installed per default. However when installing steam, you should be prompted to chose a vulkan driver. vulkan-radeon was the correct driver to install.
In case of Nvidia hardware, vulkan drivers are installed per default when choosing to install the Nvidia driver because Vulkan is contained in the proprietary bloatware blob that is their driver.