Fwiw I've been using react on the frontend and php on the backend for like 8 years now. It's a multi page app. It's fast. No issues. If you want to swap php for go it'd be just as easy.
Interesting. How do "break down" react to be multipage. With next atleast the folder based layout (and the [id] naming convention) I found helpful. Disclaimer I'm still a react noob.
In webpack, if you use a simple dynamic `import()`, it will compile all the files that it might possibly match. Then in PHP I just pass down the name of the script I want to load plus a bit of server-side data and render it. You can fiddle with the webpack settings about how aggressively it will code split or re-use libs. I recommend throwing all the vendor/3rd party party stuff/rarely changing libs into a single package and set a long TTL. Then the first time a user visits it can download all that junk and from then on they only have to re-download the bits that you change. For me, I might change a few pages a week. For my day job, we deploy once a day, M-Th, so even then if a user visits 100 pages in a day, they only pay for the JS on the first click of the day, and only the parts that have changed for the most part.