Subtotal syntax should allow function name in addition to the existing number system. The syntax of Subtotal is: SUBTOTAL(Function; Range) For Function, there is a list of numbers which references to the allowed functions. See help: https://help.libreoffice.org/Calc/Mathematical_Functions#SUBTOTAL To simplify the manual use of the syntax in Calc's input line (without look to the help page if you use this function rarely), allow to use the function name too. In addition to the example on the help =SUBTOTAL(9;B2:B5) is should be allowed to use =SUBTOTAL(SUM;B2:B5) or maybe another notation (which is more logical for a rare subtotal user like me) =SUBTOTAL(SUM(B2:B5)) There may be technical obstacles against it but maybe it's possible without too much effort.
CC'ing Eike Rathke as Calc specialist.
Maybe an easy way would be listing those in the help text on the function wizard. If a manner can be I think would be as in the CELL() function with the required function name as text inside quotes. In any case a request for enhancement.
All three approaches are not viable. Using a stray function name within an expression would be a completely exceptional case to all formula parsing, SUM is a function name that expects opening parenthesis, argument(s) and closing parenthesis. For the same reason in SUBTOTAL(SUM(B2:B5)) the result of summing the range B2:B5 is the argument to the SUBTOTAL function. Literal text as arguments does not play with translated UI functions. Furthermore, but not least, SUBTOTAL is *defined* by two standards to have the first argument as a function number and all spreadsheet applications interpret it as such. Won't implement.