how to calculate the probability to be homozygous?

My solution from post#3 yields the same result as OP's post#4, after summing the partials as instructed:
(Bear in mind, our data is rounded to 3 significant figures because we're copying from a picture. )
This is why C2 shows "1.08" instead of "1.07".

Row\Col	B	C	D
2	3.28E-05	1.08E-09	=B2*SUM(B$2:B2)
3	4.09E-06	1.51E-10	=B3*SUM(B$2:B3)
4	4.06E-06	1.66E-10	=B4*SUM(B$2:B4)
5	4.08E-06	1.84E-10	…
6	4.08E-06	2.00E-10	…
7	8.68E-06	5.02E-10	…
8	4.48E-06	2.79E-10	…
9		2.56E-09	=SUM(C2:C8)

Each entry is multiplied by itself PLUS all preceding entries.
To fit the layout in your picture, paste this in D4 and copy down:
=C4*SUM(C$4:C4)