I know that the answer depends on what kind of side projects, but it can be useful to have a go-to stack that you are familiar with and can use without much thinking.

Otherwise there is always this huge risk of going down the rabbit holes of searching what is the optimal tech stack and wasting precious time instead of building something and focusing on the problems faced by your users.

RoR? Django? Serverless? No-code? And how do you deploy it?