In Adobe Photoshop 2021 (October 2020), the Line Tool is no longer a rectangle with a width of x pixels, instead it is now just a line that has to be stroked to be visible. The fill now seems to be superfluous.
Here is the feature summarized in the Adobe release:
Line Tool: You can now use the Stroke option to govern Line Tool line thickness instead of previously using Weight. With this change, using the Line tool in Pixel mode has been disabled.
Whether or not you thing this is a good approach, when I create a new line, it is not visible even when you stroke it. How do you make the line show up?