Depends - what are your dc’s favourite subjects and are they the same ones they are good/best at?
For example - my ds has severe dyslexia (along with dyspraxia and dysgraphia) but is great at maths so is currently rocking maths and further maths a levels now her is in y12, having got 9 for both at gcse and predicted A* for A levels. But I know lots of kids with dyslexia also have dyscalculia so maths would be a rubbish choice for them.
He’s also doing physics and computer science because he enjoys the maths within them too but also because he realised that computer science has a project that you had to do in y13 which he has chosen to do as he liked the thought of backing some marks in advance that weren’t dependent on exam performance - he is good at putting his mind to something and doing it, so I suspect he will do very well at it when the time comes (unlike his non-dyslexic brother who did badly on his GCSE subject that involved a long project because he just never managed to get into it).
Make sure when he starts in y12 that you talk to the senco to make sure that he has his dyslexia registered and find out what help or support they can provide during lessons and in exams, so that he has it all the way through - eg Ds uses a laptop to type his exam answers because teachers couldn’t read his writing - apart from maths as it’s easier to do that actually in writing compared to on a keyboard, but he knows he has to be really careful about what and how he writes to ensure it’s legible. And luckily because he is good at maths he has time to go back and check it all through and rewrite bits that aren’t clear enough. But they are happy to let him do this for exams because he had the documentation from earlier in school and it wasn’t something new introduced just before the exams.
worth asking if the need any different info or documentation for his a levels so that you can get that sorted and put into place early. (Hopefully you have this in place already for his GCSEs!)
if there are any courses he enjoys then figure out how he enjoys learning and see if you can use any tech to support them - over the last few years there have been massive advances in for example AI can be used to create supporting materials, flash cards, dyslexia friendly summaries, PowerPoints etc that might really help too - try variety and figure them out early to get best use of them and work out if there any other thing that will help - having a large timetable on the wall, having files to put all ongoing support and revision material in and so on…