Well tropes become racist when they're negative stereotypes or literary ideas only prescribed to characters of a certain race because that is the perceived notion or underlying racist views authors have of people of that race. I don't think there's anything inherently wrong with a character being a tech wiz, a ninja martial artist, a crime lord or having a mystical/spiritual connection. But it shouldn't be the only thing that defines Asian characters, and that's largely the problem.
Asian characters in the MCU so far consist of Wong (mystic), Helen Cho (a scientist), Ned (a stereotypical nerd), Trevor Slattery/faux-Mandarin (an actor/criminal), and the Ten Rings guys (terrorists). That's not great representation at all, the only one that might not even be a stereotype is Slattery (but he's a joke of a character). At least Wong is funny and portrayed far better than his comic book counterpart (as Strange's equal and not his kung fu kicking manservant) and Ned seems to be having a love life (which is great for kids who look like him).
The problem is when those are the only images that are shown about Asian people. Think about why Shuri and Okoye became breakout characters: the images of a black or African girl being a science and tech wiz and the image of a strong, black, bald and proud female warrior in a blockbuster is not something you see often these days. It's why Crazy Rich Asians took off in the US and was a big deal for Asian Americans, because they often don't see Asians or Asian Americans be in romantic comedies living lavish lifestyles and pursuing love lives (and being very good looking and desirable). When minority people have been fed the same images for a long time they start to desire something more, and that's how BP and CRA became huge.
Marvel can (and should) keep Shang Chi as a martial artist and Zheng Zu as an evil schemer, but they need to
add things to those stereotypes that at least make them feel more like people and actual characters. I'll talk a little bit more about what to do with Zheng Zu below but things that can help Shang Chi (as said earlier) include making him desirable, giving him romantic interests, and a great and relatable personality and character arc. For Zheng Zu, show that he does genuinely both Shang Chi and his mother and has healthy relationships with them (despite his ways unbeknown to them) rather than being an abuser or seducer. And give him a complex yet understandable motivation for why he does what he does.