I dislike posts like this. Technology moves quickly. PIs are great for hobby electronics where you need a little computer. Want a cheap computer to run a few things 24/7 and know what you're doing? Pi it is. You don't need to run containers on a pi because you have the skills to install the dependencies manually. They cost pennies to run 24/7.

I think of pis as beefed-up calculators. I have made lots of money using a pi zero running code I needed to run 24/7. Code I developed myself.

Having an old laptop with outdated parts taking up lots of space, weighing a lot, and having components like fans, keyboard, and mousepad most-likely soon dying and needing replacing is an additional concern you don't want.

Someone below saying use an old laptop if you're living with parents and don't pay the electricity bill is a bit lame. Do your part for the world. Someone will be paying for it.

Ultimately, use what you want but if you're just starting with servers, use a virtual machine on your computer and log in to it. You can dick about with it as much as you want, and reset back to a working state in seconds.