I know it's cliche to say it, but most of the tech debt I've seen is on the frontend.
Most backends are relatively simple. Just a DB with lots of code wrapping it. But even the worst backends are relatively simple beasts. Just lots of cronjobs and lots of procedural code. While the code is garbage, it can be understood eventually. The backend is mature... even the tech debt on the backend is a known quantity!
But the frontend... damn the complexity and the over engineering are something unique. I think there is a fetish among frontend developers to make things as complicated as possible. Packages galore and SO MANY COMPONENTS.
As soon as people start inventing their own design system, UI framework, and sub packages I think the frontend is doomed for that project.