The scrollbar is typically defined by the system/browser, and not by an individual application and afaik we don’t do anything special to it.
That’s not very straightforward to do and we are in general (as an industry) moving away from modals.
If you look again at your screenshot, you can actually see the 7th tag appearing at the bottom, indicating there is more below. You can also search instead of scrolling, to find the tag you want.