I don't really recommend isomorphic environments, but if it's your cup of tea, Tanstack Start is making a lot of progress. It removes all of the magic and misdirection of Nextjs and just provides a good light alternative.
Issue with all things tanstack is they change everything constantly. The Tanner guy really does make decent libs but he drops em pretty quickly for others to take up maintenance on which makes it risky to pull into any production app.