I am once again asking for your assistance: how do you add a comment like this to a focus.

They work using custom tooltips. That one is done like so:

custom_effect_tooltip = unlock_warsaw_uprising_tt

To create a custom tooltip, you will need to either create your own localisation file, or add to one that's exported with your mod, and it would look something like this:

your_custom_tooltip_label_tt:0 "Whatever it is you want to say"

And in your focus you'd have:

custom_effect_tooltip = your_custom_tooltip_label_tt

Obviously, you can change "your_custom_tooltip_label" to whatever you want to refer to it as.

As for colours, formatting, etc. of the text, you will probably want to reference the wiki:

https://hoi4.paradoxwikis.com/Localisation#Formatting_characters

https://hoi4.paradoxwikis.com/Localisation#Functions

Just as an example of formatting, in case those links don't make too much sense, this is what the tooltip in the image looks like in the localisation file:

unlock_warsaw_uprising_tt:0 "With §R50% Resistance§! in [POL.GetFlag] [POL.GetAdjective] states, you gain access to the §YWarsaw Uprising§! operation after completing the §YMake Resistance Contacts§! operation."

I will try doing something