Is resorting to medical technologies to determine the sex of a fetus as male, when one already has two daughters, considered an objection to Allah's decree and destiny, or is it among the permissible embellishments that have not been forbidden?

There is no harm in determining the gender of the baby if the Sharia-compliant controls are observed. This does not contradict contentment with divine decree or the Quranic verse, for all of that is by Allah's will and قدر (predetermination). There is no harm in seeking the adornments of this worldly life through lawful means. It is better for a Muslim to be patient and leave the matter to Allah, for He knows best what is in the interest of His servants, and good may be found more in females than in males. Masturbation must be done by the wife's hand when necessary.