Sure. Any concrete implementation detail constrains your architecture and freedom to some extent.

But VS Code first and foremost uses a web-browser for UI. How much does the choice of a UI-technology really constrain the rest of your application and its architecture?

I would argue that with a good architecture, the choice of UI-platform should place near zero effective constraints on the rest of your application, how it's structured and how it performs. It should certainly not be a critical component of your overall design, it should be an implementation detail.

Are you arguing otherwise? Can you come up with some concrete examples where the choice of UI-library causes troubles other places in the application? If not, it seems you're more or less agreeing with my original statement.

And as such, I don't see any fundamental problems using a web-browser in a text-editor.