we can’t because they’re long dead

If someone died today who was owed £100,000 for some work they did, would the debt be written off, or would it become owed to their estate?

most British didn’t have slaves

Did you forget what thread you were commenting on? This is about the royal family, not some random East Londoner from the 17th century.

am I owed restitution

I would say so, yes. But it’s not “moral”, this is nothing to do with morals, it’s to do with the reality of the situation - Irish people have historically been victimised for the benefit of others, especially the British, and so I would 100% be in favour of the UK making some sort of payment to try and mitigate that problem. I do have to say that, morally speaking, (but not technically) I think it’s lower on the priority list, because white Irish people have a pretty decent quality of life now, and imo it would be better to try put money where it would be most needed before paying overdue debts to more prosperous people