How do I make all incoming emails go to the Inbox and eliminate categories in Apple Mail?

Are you using a Gmail email address? Is so, or for any other IMAP email provider, the Apple Mail app just syncs the organization of the Mailboxes seen on that email providers server. Specifically for Gmail, you can change that by signing into your account with a web browser and changing the settings for the organization.

https://support.google.com/mail/answer/18522?sjid=8025646427425909276-NC

More information about the use of Categories for Gmail accounts is available from Google here:

https://support.google.com/mail/answer/3094499?hl=en&co=GENIE.Platform%3DDesktop

If that is not the issue, then let us know who your email provider is and confirm you are using the Apple Mail app along with Mac OS 15.7.

Depending on whether you are referring to the Mail app on an iPhone or the Mail app on a Mac... you didn’t specify.

On macOS 15.7 click on the View Options ⋯⃝ symbol and deselect Show Mail Categories.

Please note that you have two different responses from users because you didn’t fully explain your issue. In the future be explicit and fully explain your issue in detail.