Extra time/scribe/laptop in GCSEs??

If you have a scribe you can write some of the answers yourself. The scribe would have to fill in the coversheet to state which questions were done by the candidate and which were written by the scribe.
If your ds qualifies for a reader then for some subjects and some SEN it is possible for the reader to read the writing back to the candidate. But the candidate has to make any changes, this cannot be done by someone else. If somebody else were to alter the script that would be regarded as malpractice and the candidate would be disqualified. (There may also be penalties for the school as well).
If you required a reader, you would be in another room too.
It is usually possible to take a lap-top into the main exam hall. You would need to be seated near a power-socket but otherwise you would be treated the same as everyone else during the exam. (You may also need to supervise your work being printed out afterwards).

www.jcq.org.uk/wp-content/uploads/2020/08/AA-regs-2020-2021-version-for-website.pdf

When is he due to sit gcses? Deadline for access arrangements next summer is end of March.

Have a look at JCQ guidelines for advice and qualification for any adjustment as this can change from one year to next. I've not heard of a transcribe. Why is he resistant to using a laptop? The adjustment has to be one established as being used in tests and lessons.

Just before my ds did his A-level (mocks) he was in an accident and couldn't write, so the school gave him a scribe for each of his exams (fortunately his mocks, not the real things). Beforehand, he thought it would be excellent, but in reality he hated it.
The scribes couldn't spell the words he wanted to use, he had to dictate grammar and the like which he normally wouldn't think about, and he found it incredibly stressful and hard to maintain his 'flow'. I don't know enough about it, but think there is something in the theories about having to 'write it yourself' to be able to reproduce those thoughts.
It isn't necessarily the answer for everyone.
In your ds's case, I'd have thought the fact he uses a laptop in class usually would mean the best thing is to use his 'usual mode of recording'.

I've never heard of that and I think there might be issues around security possibly?

My ds had a scribe for GCSEs and he found it helpful for eg English and geography. Didn't bother fir maths.

yy student has to spell out words and specify punctuation in order to gain the marks for that element -scribe then has to sign to say that they did this. So it's a bit laborious (ds didn't do that, he is not a high achiever).

A friend's dd who IS a high achiever, but had fatigue issues, was offered a scribe and found it tricky for reasons above. I believe she used it only fir essay heavy exams such as history and eng lit.

I agree, laptop may be easier?

He would have more control using a lap-top than a scribe in my opinion.
Why is he reluctant to use one in mocks and exams?
For the scribe he would be expected to spell out any specialist words by letter and also dictate all punctuation i.e. full stop, comma, new paragraph. I think you also have extra time because this slows things down. He would also have to be in a room by himself with the person doing the scribing and possibly an invigilator as well. The scribe can't be someone with specialist subject knowledge - would usually be TA/HTA.