Indirect formula function: can a cell with a formula as text be interpreted as a function by a different cell?

Similar to this question here, is there a way to do the opposite of the FORMULA() function?

In other words, if a cell (eg. A4) has the syntax of a formula entered as text:

'+sum(A3)'

is there an indirect way of having this text be interpreted as a formula in a different cell?

=UNKNOWN_FUNCTION(A4)

which would then calculate the sum of the cell in A3

There is no function for that.