What is the ruling regarding a female who underwent a sex change operation and lived as a male for a long period, then was guided to Islam: is it permissible for her to go to the mosque and perform Friday prayer with men?

Praise be to Allah for guiding you to Islam. Allah has forgiven you for all your past sins, including the gender reassignment surgery. You have begun a pure, clean slate, so preserve it and ignore the whisperings of Satan.

Allah created you as a female, so you must accept this and return to your original natural disposition (fitra). We asked some doctors, and they informed us that this is easy, so return to specialized doctors. If the uterus has been surgically removed, it cannot be repaired, but there is no sin upon you because Islam nullifies all previous sins, as does repentance.

As for your mingling with men and attending congregational prayers and Friday prayers with them, this is not permissible because you are female, and you must adhere to the rulings of Islamic law specific to women. However, there is no harm in mingling with women. If mingling with them would cause you embarrassment due to your appearance as a man, you may postpone it until your outward appearance is changed. You must take the initiative to go to a doctor to correct the mistake. Until then, you can learn about Islam through books, articles, and lectures.