That depends. Puberty blocking _generally_ (*not always) is not unreasonable for a period of time because it “pauses” development enough for them to get their act together to decide better and be more certain.
They’ve been in use for decades for precocious puberty because puberty too young is torture for them. They can’t physically/emotionally handle it and with gender dysphoria, it is very similar.
However, if it was therapy such as whatever they use to encourage development one way or the other in sex, then yes 10 would be probably too young in most cases.