i never understood why he is absent at the end of episode 26 of eva tv, and if eva tv is supposed to take place during the end of evangelion then why kaworu doesn't appear at the end or during episode 26 of eva tv?

1. Because he's not "human."
2. Because his absence by Shinji's own hand is fundamentally why Shinji is spiralling in the first place.

Same reason the Jet Alone guy isn't there, he appeared only in one episode.

at the point EoTV was made no one knew he'd be such a fan favorite/ breakout character that ppl would desire closure for.

Hence his bigger role in EoE, the Manga, the Rebuilds, and all the spinoffs.

Even the idea that he has Adam's soul was probably not fixed at this point - (for example his character design was originally meant to be a mix of Asuka, Rei and Shinji since they were mindprobed by angels, and his line to Rei about "taking the forms of Lillim" was only added in the DC episodes)

^^^^
That's a really interesting take. In NGE, Kaworu really seems more of an "angel-type character" (appears in one episode, starts a conflict, and is eventually defeated). As I said before, I see his character as a twist on the monster of the week formula. Like all angels, he takes on a unique form. But because he not only looks and acts like a human, but also bonds with Shinji, it raises a lot of moral and philosophical questions regard killing him. It also feels very personal for Shinji as a result.
Anyway, as for his appearance, I do remember reading that he was actually modeled after Shinji, Asuka, and Rei.I also know that Anno made him a boy because Kaworu was supposed to be an "ideal" version of Shinji (someone Shinji could look up to and throw himself in)...