Currently you have to do it near enough the legacy way, double click an asset, find the material in the content browser and then apply it with the backward arrow (currently around 6 clicks and a little finding of materials).
Surely there are ways to speed this up, even more so when working with a large amount of assets:
Click and dragging a material onto an asset within the content browser (Not the world) could by default apply it to material ID 0. Even more so it could present a window specifying “Are you sure?”/What material ID would you like to apply it to (Click and drag could be 400% faster).
Selecting all of your meshes in the content browser, right click and a new option of ‘Assign material to ID slot X’ in which the following click would have to be the material you are wishing to assign (3 clicks or so, 200% faster).
This slowdown is most noticeable with atlas mapped modular environments, where you have multiple assets sharing the same material. But would at least shave a few seconds per each individual asset.
For example bringing in a modular set consisting of 20 or so assets that share a 2K texture, you are looking 120 clicks at least and quite a few minutes applying materials, instead of possible seconds.