If you spend time creating new modern pages in SharePoint Online, you’re used to seeing the Web Part Toolbox laid out in an alphabetical order, which often means a lot of scrolling if the items you use frequently are towards the bottom… we’re looking at you, Weather web part…
But help has arrived… The Web Part Toolbox is now grouped by web part types, and it also uses machine learning to put the ones you use most frequently up at the top. Here’s how it looks…
When you click on the Plus icon for the Web Part Toolbox, you’ll start to see the changes. First, you’ll see the Frequently Used section, which is specific to the web parts you use most frequently:

Followed by Text, media, and content web parts:

Documents, lists, and libraries web parts:

Feeds web parts:

News, people and events web parts (what happened to the Oxford comma here, Microsoft???):

Data analysis and Regional information web parts:

And finally, the Advanced web parts:
