It's "replaced" already under Settings -> Storage -> Disks & volumes. When doing it through File Explorer the old one gets called because File Explorer is still (largely) a legacy style app.

I actually quite like the new UI as far as the replacement of the format dialog but the portions that replace the Disk Manager functionality are a bit lacking because it doesn't have the graphical representation of the disk layouts.

Default view: https://i.imgur.com/56yZ8gZ.png

Advanced view section: https://i.imgur.com/fKb3R8c.png

Formatting an existing partition: https://i.imgur.com/DmbX3FQ.png

It's not perfect but it does largely retain the same layout while matching with the OS theme and adds a few options that used to be multi paged wizards in the disk manager. Minor things like "format" is a bit more direct than "start" and "cancel" a bit more apt than "close" sneak in as well. I'm sure it being 33% wider will be the end of the world to someone though.

One thing I think I'm a bit split on is it still expects you to enter new partition sizes in MB. It does at least add localized number separators but it seems a bit silly to worry about how many millions of megabytes given the numbers will only grow with time for here.

Format needs an update. We are getting the update ready for you . . .

I think it's really sad they replaced the disk defragmenter UI. It was nice to look at the blocks being moved around. Worth keeping a spinning metal hard disk just for that.