In my experience as a web component library builder, writing and maintaining web components is the easy part.

Getting them to work well in various react and angular codebases is not easy. New versions of React work well with web components. Old version s of react need web component wrappers. Angular works out of the box with web components (aside from some quirks and sometimes encapsulation issues with the web components). However, web component form controls will not work with angular reactive form controls and require an implementation of the control value accessor interface. So if you're a web component form controls you need some kind of intermediary layer to play well with angular forms.

Problems tend to surface with testing infrastructure as well, especially in older codebases running Jest or other jsdom based testing frameworks that don't recognize the web component apis well (shadowDOM, elementInternals, ect). Upgrading to vitest with browser mode can solve these problems, or writing lots of mocks.