If you complete a bank transfer, to fund your ISA, before midnight on the 5th April but it doesn’t actually reach Freetrade for a few days, which tax year will the deposit fall into?
If by “reach” you mean arrive, it counts on the day it arrived. When you send it is irrelevant. As bank transfers are now ordinarily instant, though, it should be fine.
I assume you meant the 6th, not the 5th.
My understanding is that the money must arrive before midnight.