As a backend, how do you do your sideproject’s front end?

A frontend does not require JavaScript. I've made quite a few useful MVPs and internal tools whose frontend solely consists of dynamically generated HTML pages served via a Python Flask server with Jinja for templating or a Go server with its native template/html package for templating.

If you want to polish the UI a bit consider throwing in some simple CSS—either handrolled or prebuilt with Bootstrap or Semantic UI.

This reply assumes the project serves the UI over the web. For applications that are not hosted apps, I've had CLI tools just spin up a local server with the UI for a quick proof of concept UI.

It depends on what you're building, but I've managed to make a lot of nice services with pretty minimal Javascript. This is obviously not possible for many types of services, but if you do need it, you could keep trying new frameworks until you find one that really works for you, or perhaps have someone else help you out or work on the JS.