In 2002, changes were made to the Constitution of Monaco which excluded adopted children from the line of succession.

Succession to the Monegasque throne

Regarding the Japanese throne, quoting Wikipedia:

In July 2026, legislation was passed to allow the adoption of former male members in the patrilineal line. Although the adoptee is not eligible to succeed the throne, his male patrilineal descendants are eligible and the order is determined by their natural birth order. Yet, the debate still remains and currently no former male members have been adopted in.

It's anybody's guess exacting what the bolded by me words mean. If the current emperor adopted somebody, does that phrase mean the adoptee's heirs are placed as if they are biologically descended from the emperor, or does it mean that they are placed behind those whose succession rights were acquired at birth?

Japanese imperial succession debate