Running Minecraft on Windows XP

This is a small guide to help you run Minecraft on Windows XP (and Vista) in the best way I know.

Getting started - Update your OS

First of all, and this is very important, you will need to make sure your XP installation is fully updated, especially with TLS 1.2 and Certificates. Updating your OS beforehand will not only fix possible problems while setting the game up, but also ensure maximum possible security.
In order to learn how to update your system, make sure to read Using Windows XP in modern times.

Step 1 - Install Java

Obviously this is one of the most basic yet important steps, you can't play Minecraft Java Edition if you don't have Java installed.
Now you can go the easy way and get the outdated Java 8u152, which I'm sure isn't even advertized on the Java website anymore, but you can also use the Windows 32-bit version of OJDKBuild 1.8.0_322 which works fine on XP. Build 322 is a lot more recent than 152!
Now that you have either version of Java installed, you can advance to the next step, which is choosing a launcher.

Step 2 - Launchers (and the fuss with Microsoft accounts)

You have likely heard this many times: the Legacy Minecraft Launcher was discontinued due to Mojang's recent switch to Microsoft accounts. Now that the migration is basically over and users that don't want to switch will have their accounts disabled forcefully (or so I was told), the Legacy Launcher is unfortunately no longer an option.

However, we are not limited to just the official Minecraft launcher. There are many third party launchers that work just as good, or even better. Many people prefer MultiMC, but unfortunately the latest version of it does not appear to play well with Microsoft accounts. While older versions do tend to work, digging them out is painstaking and likely not worth the effort to mess with, plus they will probably become outdated at some point.

I would instead use a launcher known as TL (don't confuse it with TLauncher, they're completely different things!), developed by turikhay and available at tlaun.ch/jar.
This launcher is great in that it supports official Microsoft accounts, old Mojang accounts, as well as "cracked" sessions and ely.by skins. Whatever your preferred way of playing Minecraft is, TL likely has you covered. It's also easy to configure and customize!