I have a 2020 RTL and a service manual, but you might be a little dissappointed in what follows.
That light is called a "signature light"; it is, as you probably know, an LED display rather than a bulb. I believe the part number to be 710006812 & it's about $140.00. Two screws, from the back hold it into the formed plastic nose of your RTL; if you if you search an OEM parts website you can check it out.
The service manual that I have is a downloaded version; I could not find a copy in print at the time. This manual describes the procedure for testing the function of the signature light circuit from the connector plug under the right side "fang panel" where the frunk module joins the main frame; if it fails testing, the manual simply states, "repair circuit" (nice, huh!) I see no step by step description of how to get to that light in the lighting section and the body panel section only gives only details how to remove the entire frunk module. All I could find is an exploded view of that module; nothing that serves as guidance.
In looking at your pic, it appears that the other signature light is functional, so I would say any testing is moot. My guess is that the display is bad, in and of itself. If you want to trouble yourself and foot the bill for what should be a BRP "warranty covered" part; best wishes.