Allocate funds to various "accounts" based on maximums

I'm probably wrong but if your intention is to adjust the % allocation (C2:C7) automatically (?) then you have a circular calculation, no ?

value * % allocation

is circular given % allocation is dependent upon value and value is itself dependent upon % allocation

it follows also that altering C2:C7 would affect prior calculations

It might be a good ideal to outline the workflow for all of the values in your file ?

I suspect you will want to have Max Balance, Opening Balance (static) - Current Balance needs to be separated from the actual allocation calculation (to avoid circular).

It may then be the case that you will want to perform additional calcs. adjacent to the transactions to determine adjusted % allocations to keep things as simple as possible.

To outline the complexities that I think you face, consider:

1000 is assigned to a specific category X which has only 50 remaining balance (to Max)
It follows that the remaining 950 needs to be apportioned across the other categories.
Then let's assume that the other categories (ie ALL less X) cumulative % is 90% (ie X allocation is 10%)

Let's further assume one of the remaining categories Y has an individual percentage allocation of 45% - ie 50% of the remaining 90%

Our instinct will be to say that Category Y should be apportioned (50%) 475 of the 950 remainder.

However, if we then say that Category Y can itself accept only up to 250 (to Max) then you can see how things are going to get increasingly complex.
(ie the remaining categories [excl. X & Y] need to apportion the remaining 700 based on their relative % regards the remaining 45% and they too may not be able to accept full apportionment)

Hopefully I'm wrong and it's much simpler than the above but that's my initial reaction to the question.