This is always a tough decision to make as it is difficult to switch from one style to the other if you decide to do so in the future.
I think another important question to ask is if you plan to have any other client for your application (maybe a mobile app, in addition to the web app). If so, then a separate Laravel backend is probably the better choice as you can use it to serve data to all your clients. For the web client, Next.js is a great choice if you're familiar with it and React.
If it's just a web app, I personally am more comfortable working in a "full Laravel" application. I find that there are fewer things to worry about like state management, setting up auth, deploying 2 projects at the same time, managing an additional node server, etc. However, making your components interactive with JavaScript is a bit more cumbersome. You can drop in components but if you do this a lot, it starts to get a bit messy.
You can also try Inertia, which has the benefits of a SPA, but the simplicity of a "full Laravel" app. They recently launched server-side rendering, so your SEO is still optimal: https://inertiajs.com/server-side-rendering. I haven't tried SSR in Inertia yet, but it might be something worth checking out.