You can use any other language on the server side. What would be good is if wasm had full access to the DOM instead of through some JS layer. Or maybe a new browser is created that did away with JS altogether. It's always been my dream.
Cloudflare workers if you want JS/TS.
There is no _the_ alternative.
But there are alternatives. I would reach for Go. I’m not great at it but good enough that I know I can code up a server. And I know it will be be stable and simple to deploy - upload the binary and run it via systemd.
Yes! I was inspired by levelsio's use of PHP but I don't want to use PHP. I was once enamoured by Python but it still hasn't fixed it's dependency management problems. Go occupies a nice place with the simplicity of Python but with static typing and better tooling.