Everything served under one domain doesn’t have to use one technology.
Use backend rendering when you can, use HTMX where you need a little bit more, use React on the actual bits where it matters.
As a side-benefit, the React bits might end up less complicated as React doesn’t need to handle every single use case.
Good old server side rendering is simple in Rich Hickey's "Simple Made Easy" way. You can build more complex logic on top of a standard server rendered model, but the base model is mostly dead simple to reason about. I like that. I've built web "apps" in AngularJS, React, Reagent (ClojureScript) and Next. So I'm not coming at this from a grumpy "backender" position. I'm coming at this from having done lots of frontend stuff and finding the frameworks becoming increasingly complex beneath the surface. It feels like they are targeting the "easy" in Rich Hickeys parlance in the sense that you don't have to write a lot of code to make something fancy. But reasoning about the behavior and what actually happens in the framework when something doesn't work is increasingly difficult.
Edit: And maybe this is a "skill issue". If you just learn the framework and library well enough you'll get by much better. But I tend to not want to bind myself to any single framework too much. So simple frameworks that don't churn too much is better for me.