Each designers, each foundries, attend to their font licensing in their own way.
It can be tricky to completely understand what you can and cannot do with a font once you've purchased it.
That's why most font distributors give you an access to their Font License, commonly known as the EULA, on their website.
This document can sometimes be tough to go through as it's a lot of legal stuff but it's super important you have a look at them before using a font in a project — you might get in trouble if you don't respect an EULA and nobody wants that!
Nowadays, font licensing tends to get easier to understand. Foundries know comprehend how difficult it can be for anyone to go through a super long document like an EULA and thus usually give a "shortcut" access to the whole thing by showcasing different bullet points of what you can and cannot do.
In any case, downloading a font for free or paying for it doesn't always mean you have the right to use them on anything you want: read the foundry's EULA !
And if you're a bit lost with what you can or cannot do, simply write an email to the foundry or designer and directly ask them about it. I have yet to find a foundry who's not open to explaining the whole thing to designer.