Sum of numbers of same cell and the result will be 0 to 9 or 11, 22, 33 or 44

Hi,
I would like to know if you could help me create one formula to excel.
I would like to make a sum of each number of same cell.
The sum has to have the result of 0 to 9 or 11 or 22 or 33 or 44.
For example: If the cell has the number 911. The sum will be 9+1+1=11
For example if the number is 9996=9+9+9+6=33
For example if the numer is 23564=2+3+5+6+4=20=2+=2
In this moment I use this formula:
=If(REST(A1;9)=0;“9”;REST(A1;9)) (but the result will be from 0 to 9)
I need to add the exception if the result is 11 or 22 or 33 or 44
Can anyone help me?
I have the formula I can cover also the result of 11 but I need also to 22 or 33 or 44
=IF(A1=11;11;IF(REST(A1;9)=0;“9”;REST(A1;9)))
I have the same question in this link
https://www.excelguru.ca/forums/showthread.php?8749-Sum-of-numbers-of-same-cell-and-the-result-will-be-0-to-9-or-11-22-33-or-44
and in
https://www.mrexcel.com/forum/excel-...2-33-44-a.html
Thanks.
Best regards

*Deleted*
Misread question

It looks like you've supplied the links.

Try this

	A	B	C
1	9996	33	In B1: =SUMPRODUCT(--MID(A1;ROW(INDIRECT("1:"&LEN(A1)));1))
2	23564	20
3	911	11

Here is a non-volatile formula
Enter in B1 and copy down

Formula:

Please Login or Register  to view this content.

v	A	B
1	9996	33
2	23566	22
3	911	11
4	596969	44