How to clean up my Apple Mail window?

Birck Cox wrote:

I've had a lot of problems withApple Mail lately, most of them having to do with distinguishing "Junk" from non-junk. I have three email addresses. One is an iCloud ".me" account, one is a Google account, and the third and oldest one is an Earthlink/Mindspring account. Originally, all three could employ the main Apple Mail inbox, that is, the Inbox directly under the words "On my Mac". Now, however, after going through every inbox, and Junk folder, I find that absolutely none of the On My Mac mailboxes (inbox, drafts, trash, sent, etc.)are functional. Except for the custom mailboxes I have under the On My Mac heading, I have to rely on separate email categories for each account, thus: Mindspring/Inbox-drafts-sent-trash, iCloud/inbox-drafts-sent-trash, and Google/inbox-drafts-sent-trash. I would like to have one inbox for all three, if that is possible, preferably the "Main" inbox, first one under the "On My Mac" heading, rather than that inbox and its subcategories, mostly empty, straggling halfway down the page, followed by repetitions of the same categories, doubling the page height. Is that possible, and if so, how? I have included a screenshot of the Sidebar. PS: I am on a Mini M1 running Ventura 13.0.1.

https://discussions.apple.com/content/attachment/7d2f3f22-957b-4a0d-9050-2a7510a98678

I have no idea what to tell you specifically, however you can add or remove just about anything anywhere if you move your mouse to the right side edge to reveal +

and /or use the Control key reveal more options:

There is a help menu in the app Mail>Help you can search

ref: Mail User Guide for Mac - Apple Support