I love
Theodora! I would never use it though because I would use
Theodore on a boy.
Thea is probably my favourite nickname and I quite like
Theo too.
Teddy and
Dory are a bit more masculine to me.
Dora makes me think of
Dora the explorer but despite that it’s cute. I’m not a fan of
Theda tbh. Tee is one of the last nicknames I would use but it still works.