It is accessing e-tickets themselves, rather than the act of purchasing online, which can be problematic for visually impaired people. Navigating one's way through a ticketing app is doable, if you have the extended time it takes to do so and provided pop-ups don't appear (I know from my wife that nothing is more frustrating than one's screen appearing to have frozen when actually it is an 'accept cookies' pop- up that has appeared at the bottom of the screen without warning.).
What is more problematic is finding one's way to the ticket when travelling if it is stored in in a particular section of the app. If you use voiceover software (by which the screen contents are spoken aloud), it often involves double or triple taps to move between apps and app pages, so it is not straightforward.
Some websites are also much better than others in placing audible labels for each text box that describe what needs to be entered in there. It is very frustrating to reach box which just states 'text box' rather than, for example, 'departure station'.
It is not correct, as some have suggested above, that all tickets have a collect at station option. For example, I've just checked TPE's site, and an Advance fares for next week are only available as e-tickets.