How to expose a certain $user field in panel?

Back in the Kirby v2 era I created a plugin that showed certain data from a, well… Call it a superuser/admin, in this case it was me. My superuser blueprint contained some fields that I used to set up a subscription model; so I could easily set an end date for my customers and also an online payment link to iDeal (an online payment platform in the Netherlands).

Now I want to achieve the same result in v3; I have already been able to place the fields for a (fictitious) end date and payment link in the blueprint of the superuser, but I see no possibility to display these fields in Kirby’s panel.

Ideally I would also like to apply some (PHP) logic; only when the completed end date expires within 30 days this end date is relevant. In Kirby v2 I was able to do this well with some if and else stuff, but I’m afraid that this won’t work in a yml file.

In which direction should I look for a targeted solution? A plugin perhaps?

You can do that either via an info field or section or a custom section