Someone mentioned earlier about the two Duchies being examples of half-in and half-out. It's not a good example for a couple of reasons.
Firstly, because the Duchies were established by Royal charter hundreds of years ago, specifically for the purpose of providing income for the Royal family, mainly through property ownership.
E.g. when Charles was still the PoW, it was his income from the Duchy of Cornwall which was helping to fund himself and his family members including Harry & Meghan. William inherited DoC when Charles became King (and Charles took over the Duchy of Lancaster, as this is designed to provide income for the Monarch).
HMQ's point to Harry & Meghan when they wanted their 50/50 deal, was that they couldn't go and monetise their Royal titles on the open market to whomever they fancied. The RF would need to provide approval, to guard against the 'brand' being undermined and avoid any potential political issues as they are supposed to remain neutral. There are also legal considerations such as trademark and copyright laws on the use of Royal Arms etc.
Commercial activity isn't a complete no-no, but it needs to be in line with the RF's rules - Duchy Originals is probably the best known example of non-property activity. But this was relevant to RF activity as was produce from the Highgrove Estate as part of the Duchy of Cornwall, and was promoted as part of Charles' interest in supporting organic and sustainable farming in the UK. So not quite the same as merching pancake mix which is unlikely to have been produced from Meghan's garden in Montecito.