UPDATE (2 March 2020): The problem referred to in the article below has been fixed in the latest InDesign update (version 15.02). Use of the new Accessibility button in the hyperlinks panel is now optional, and as such is a very useful new feature.
There is currently a problem in the latest version of InDesign (version 15.0.1) which means that, out of the box, any hyperlinks that you create will not be screen reader accessible when you export to PDF. Such links will work with a mouse, but will not work at all with screen readers (tested with NVDA and several versions of JAWS, including JAWS 2020).
The problem lies with the new Accessibility panel in the Edit Hyperlink dialogue box. Clicking on the new Accessibility button opens athn Alt Text field in which you can overwrite a URL with a more human-friendly text alternative for screen reader consumption.
Alt text not optional
This would be fine if its use were optional, but it’s not. As things currently stand, all links must have some content entered into this box if they are to be screen reader accessible. But imagine, for example, having to replace every item in a table of contents with a copy of itself—a lot of extra work for no benefit at all. And there are, of course, many other instances in which you would gain nothing by adding text to this field.
This bug has been reported to Adobe, but until it is fixed, if you need to create accessible PDFs, you might want to consider sticking with InDesign version 14 (InDesign 2019).
Alternatively, any PDFs that have been created using InDesign 2020 can be rebuilt using Acrobat Pro. See creating accessible links in PDFs for how to do so.