Is it permissible for someone who has recently converted from Shiism to Islam to perform ablution by wiping over the feet and pray with hands released, given that he cannot reveal his abandonment of Shiism? And is it permissible for him to pray in Shiite mosques or behind a Shiite imam?

We praise Allah for guiding you and ask Him for your steadfastness.

Firstly: Ablution (Wudu') It is obligatory to wash the feet during ablution, while they are uncovered. It is permissible to wipe over leather socks (khuff) or thick socks. If you fear uncovering your feet, perform ablution away from prying eyes, or wear leather socks or socks and wipe over them. If that is not possible for you, wipe over your feet and perform tayammum (definition) (dry ablution), by analogy with someone who cannot wash a limb due to an open wound. Tayammum involves striking the ground once, then wiping your face and then your palms. It is valid on any wall or ground that has dust. If that is difficult, then suffice with wiping over your feet, following the opinion of some of the Salaf, as you are in a state of necessity.

Secondly: Placing the Right Hand over the Left in Prayer Placing the right hand over the left in prayer is a Sunnah (definition), and it will not harm you if you leave it and let your hands hang loose.

Thirdly: Praying Behind Someone Who Seeks Help from Other Than Allah or Holds Disbelieving Beliefs Prayer is not valid behind someone who seeks help from other than Allah, or disbelieves in the Companions, or slanders the honor of Aisha, or believes in the distortion of the Quran, or holds beliefs in "Al-Raj'ah" (the return) or "Al-Bada'" (divine change of mind); because these are disbelieving matters. Pray in your home, or in their mosque alone, or lead them in prayer. If you are compelled to pray behind one of them, then pray behind him with the intention of praying alone, and follow him in the actions (bowing, prostrating, and saying the salutations).