Having read the report, the commentary that is in there is interesting in itself - and brings up the points that have been raised in this thread. There's quite a bit of criticism of the Sovereign Grant.
I'm also pretty sure the monarchy has pretty decent accountants who can assess money as being "official duties". If they didn't do this they wouldn't be worthy of employment, as it's exactly what all large businesses do.
One comment from The Times being:
So generous have the Crown Estate’s payouts been in recent years that the
proportion paid to the royal household had to be reduced following a review,
from 25 to 12 per cent, in 2023. This year’s bumper profits indicate that when
the sovereign grant’s formula comes up for review next year moderation
should again be called for. The cause, as it was two years ago, is the vast and
unexpected profits being generated by leasing the UK’s coastline to offshore
wind farm developers.
And from page 18 of the report, some criticism of the linking of Crown Estate profits with the Sovereign Grant.
One partial critic was the former Cabinet Secretary, Lord Turnbull, who
described the link between the Crown Estate and Grant as “pretty artificial”
as there was “no relationship between the net income of the Crown Estate
and the funding of the monarchy, and there has not been since 1760”. Rather
the Crown Estate surplus was being used as an “index” to “uprate” the Grant.
He added that the revenues of a property company seemed “an odd
benchmark to determine the appropriate level of funding for the monarchy”.
Lord Turnbull said it would have been better to use some index of inflation, pretty much as we have done for decades with the BBC licence. We would thereby avoid perpetuating or even entrenching the confusion between the Crown Estate and the Crown itself. It all looks like someone being a bit too clever by half.
The Financial Times also criticised the Grant in an editorial entitled “Casino
Royale”. This argued that the arrangement resembled generous
performance-related pay plans agreed by corporate boards: “[W]hen the
Crown Estate does well, royals win; when it does not, taxpayers lose [...] The
perverse incentives in this system are nothing short of frightening.”
There's more, it's an interesting read!
https://researchbriefings.files.parliament.uk/documents/CBP-9807/CBP-9807.pdf