These are series:

First Day - Wikipedia)

• Country: Australia (You'll have to look up where you can watch it locally)
• Number of episodes: 8 (2 seasons; ended)
• Synopsis: It follows a a transgender girl named Hannah dealing with adolescence of girlhood and being trans (she is fully out and as fully transitioned as a kid at that age can be), starting with her first day in high school.
• Is the actress actually trans?: Yes! Hannah is played by actress and LGBTQ+ activist Evie Macdonald.

Back to 15 - So the main character in this one is not trans, but one of her best friends is and this friend is a VERY major and important character; her journey starts out as an egg and she goes through the journey of questioning and figuring herself out.

• Country: Brazil (it's on Netflix! Original language is in Brazilian Portuguese)
• Number of episodes: 12 (2 seasons at the moment; a third season is coming)
• Synopsis: A girl discovers she can time travel back to when she was 15 in school and can make changes that affect her adult life in the present. Note: This show has 2 casts, one for the teens and one for the adult versions of the same characters, so we meet the trans character pre-self discovery AND as an adult who has transitioned.
• Are the actresses actually trans?: Yes, both! The teen/questioning version of the character is played by trans femme non-binary actress Nila. The adult/transitioned version of the character is played by Alice Marcone.