Railcard, buy a physical one, or an online one?

[Appalonia]

I'm nearly 60 ( no I can't believe it either...) And one benefit is that you can get a railcard that gives you a 30% discount on train travel. However I'm not sure how it works if you buy a paper one, then try to buy a ticket on Trainline? Or, you buy it online and then buy a ticket at the train station. I've not managed to find an answer online, so I'm hoping someone on here might have an answer? Thanks in advance!😁

I prefer having a physical one, because of phone charge etc, but either is fine.

I've got the digital one.

I buy a physical one, but I buy it online and get it sent to my home. I buy rail tickets online and collect them from a machine.
The digital one has to be linked to your phone so you can't let anyone else use it. Sometimes I lend my physical card to my sister so she can save money (she only travels once or twice a year so not worth getting her own card). I know that's against the rules but rail fares are enough of a rip off that I don't care.