Returning HTML sounds like a styling nightmare, if anyone changes the structure, unintended consequences. Plus it’s difficult to reason possible states of the UI with fragments sitting on the server, possibly dynamically built on the server. Very jquery/PHP ish. I had my fun and don’t want to go back.
Clearly you haven't used something like HTMX. Do you understand what "returning HTML by the server" mean? You are basically sending back a view, like you would in any other framework actually. This would be the exact same pattern as displaying or dynamically adding a new component from either React or Vue. It doesn't create any styling issue at all, nor any unintended consequences.
To "get" HTMX, you have to think server-first. State is persisted on the server and all state-change logic is performed on the server (often triggered by http requests from a "dumb" client).
If you hang on to "possible states of the UI" that are client-side only then yes you'll have some difficulty implementing server-generated HTMX responses but more importantly, when your client has state that sometimes isn't in sync with, or shared with, or validated by your server, you're setting yourself up for errors and bugs that will exist regardless of framework.
In short, HTMX forces you to apply "single source of truth" concepts to your application.