Why was the mass edit feature removed on iPad running iOS 18.2?

I read it was removed because they added some categorization feature. I don’t care about categorization, I just want to delete multiple unwanted emails at once instead of one by one.

If required, start by searching the mailbox by Sender or suitable keyword - and/or combining with a filtered view in the Mail App sidebar:

Flag and filter emails on iPad - Apple Support

Next, either tap the Select/Edit button at top-right of the Mail sidebar - or tap with two fingers within the sidebar; simply swipe your finger down (or up) the left-side of the message list to bulk select Mail Messages. Swipe below the bottom edge to rapidly select all the visible email messages.

Once selected, tap the Delete button at the bottom of the sidebar.