Why is it impossible to use an individual homozygous for the dominant allele (AA)

Why is it impossible to use an individual homozygous for the dominant allele (AA) in the analyzing cross to determine the genotype of an individual with a dominant phenotype?

If you take a homozygote for the dominant allele (genotype AA) and cross it with an individual with an unknown genotype, then the offspring will only show the dominant trait, and it will not be possible to understand whether the recessive allele was (i.e., the determined genotype was heterozygous).

For example:

1) AA x Aa. Gametes A are formed; A and a. Offspring – AA, Aa, the recessive trait cannot be established.

2) AA x AA, gametes – A and A. All offspring will also show only dominant characters.