Is crafting magical items official in D&D 5e? I googled it, but 90% of everything I found is homebrew. If crafting is official, how do you do it, and what can you make? Is there some sort of list or something?
There are two versions of official rules for crafting
Both require that you work with your DM. In either place that these rules appear, they are optional variants to the base rules.
Dungeon Master's Guide
The first official optional rules released appear in the Dungeon Master's Guide in chapter 6 as part of the "Downtime Activities" section:
Crafting a Magic Item
Magic items are the DM’s purview, so you decide how they fall into the party’s possession. As an option, you can allow player characters to craft magic items.
An alternative ruleset is part of the optional variant to downtime as a whole (and one I personally think is more fleshed out) that appears in the supplement Xanathar's Guide to Everything in the "Downtime Revisited" section of chapter 2:
Crafting Magic Items. Creating a magic item requires more than just time, effort, and materials. It is a long-term process that involves one or more adventures to track down rare materials and the lore needed to create the item.
What can you make?
With enough money, time, and resources the rules allow for the crafting of any magic item bar artifacts. That being said, the requirements necessitate DM input.
With either of these rules, crafting magic items requires a formula:
To start with, a character needs a formula for a magic item in order to create it. The formula is like a recipe. It lists the materials needed and steps required to make the item.
There are no official rules for how these formula are created or attained.
As such, whichever ruleset is being used, the limits of the crafting is dependent on which formula the DM allows the party to acquire.