What do they do? I’ve tried to use them, but the Anchor never formats properly. What is the proper use for them? There’s no documentation of them being added in the 2.0-3.0 phase.
As @LambdaDelta said above, we announced the addition of the anchor BB code in a Bell Tree Direct on June 14th 2020. It is used to be able to redirect you to another section in the same post by clicking on a link. You use GOTO to create the redirect, and then ANCHOR is where you want that person to be taken to when they click on it. Our Rules and Guidelines demonstrates its usage well.
I also use them in the How to Use TBTs Dodo Code Queue and Trading Fields sticky over in The Airport. In the screenshot below I've highlighted one of the instances where I used the GOTO and ANCHOR in that thread:
You can also link directly to these anchors when making posts in other threads. e.g. I can direct you straight to section three of the guide above by asking you to click this link. How I did that was adding #AddToQueue after the URL:
It is useful for people who run shops, journals, galleries, etc because it means that they no longer need to create multiple posts to create a table of contents.