Good question ... I don’t think I really identify deeply with any characters in my current verse, though Thranduil’s misanthropy and Erestor’s introvert grumpiness speak to me on a spiritual level ... As much I love my bby girl Ilya, we couldn’t be more different.
In my 20 years of writing, I did do one or the two self-inserts though, so those probably come closest to me. Back then when I had my deep Karl Urban crush haha as if that ever ended, I wrote a 400,000 words RPF series about him falling in love with a girl named Annika (which before that, I for many years considered changing my real name into because I hate my actual name). That one was brutally honest on all my flaws, from my social anxiety and eating disorder to my non-existent self-confidence.
Then a few years later, I wrote an almost twice as long romance taking place in the world of the German version of American Idol. That was a lot of fun. While Vic does have many of my own characteristics at that time too, the focus was heavily on the whole casting/reality show circus, and I even researched by going to a few castings myself. I got to use all the music that I love deeply for my characters to sing in the shows etc., so rereading that thing is still one of my absolute guilty pleasures.