How to download and install the Roboto Mono font?

You can download the .ttf files from the Roboto Mono git repo and put them in /usr/share/fonts/truetype/robotomono with this command:

sudo wget --content-disposition -P /usr/share/fonts/truetype/robotomono https://github.com/googlefonts/RobotoMono/tree/main/fonts/ttf/RobotoMono-{Bold,BoldItalic,Italic,Light,LightItalic,Medium,MediumItalic,Regular,Thin,ThinItalic}.ttf?raw=true

--content-disposition is to accept the file name from github.com (otherwise the files would have .ttf?raw=true at the end, instead of just .ttf) and -P is to tell wget which directory to save the results (the directory and any sub-directories you need to create will be created automatically)

Go to this link and click on SELECT THIS FONT. Then a dialog box appears from bottom of the page. Click on that dialog box and then hover on Download icon in the top-right corner of that dialog box. It will open a small dialog box in which you get the following options(links) :-

Use SkyFonts and Download

Click on Download option. It downloads a file named Roboto_Mono.zip. Go to your Downloads folder and extract that zip file. It will create a folder named Roboto_Mono. Open this folder. Inside it, you will find different .ttf files.

Click on each of them(one-by-one) to open it in Font Viewer and then click on Install button in the top-right corner.

Following this procedure, you will have Roboto Mono installed on your Ubuntu system.