My daughter left her physical school (after a couple of difficult patchy years) in y9. We eventually signed her up to KingsInterhigh in y10 and she sat at a desk in my bedroom for 2 yrs, camera off, and studied for 9 gcses. She got them all with v v good grades. It meant that she had some academic choices for y12. Luckily by then, she was determined to try school again and she rejoined last September in y12 and didn't miss a day.
We found kingsinterhigh fine. The teachers have an exceptionally hard job delivering online lessons to cohorts with a multitude of needs (our daughter would never turn her camera on or speak, but the chat function was encouraged and the teachers were always v kind and understanding).
They gave her a lifeline when she needed it. The alternative would have been council-provided english and maths tutoring a couple of hours a week. There seems to be a gap in provision for anxious but academic kids. I don't know why councils aren't setting up their own online schools. Well, I do know, but it's frustrating to see it not being provided.
We paid for y10 but then got the LA to divert our daughter's SEN funding to Kings as she was still enrolled at her physical school. That meant that in y11 we didn't have to pay the £3000 that sitting her igcses online would have cost.
As far as negatives go, she now speaks of the trauma of being separated from her cohort (despite her friendships having already died). So, there may be an social-emotional cost to consider too.
But we don't regret it. We did the right thing for her at the time. Good luck.