Hi partner,
This is by design.
In order to be compatible with the display effects of different devices, the unified interface automatically adjusts the layout of the form to make it easier for users to view.
The classic form editor is targeted at the web client, not the unified interface.
Here are the differences of the same form layout in classic form editor between the web client and the unified interface.


The web client's forms strictly follow the style of the classic form editor, but the unified interface does not, it will adjust automatically.
To edit forms in a unified interface, I would recommend you use the Power Apps form editor.
Go to https://make.powerapps.com/, click Data > Entities > Account > Forms, open a form.

Then you could edit this form, and its style is uniform interface, what you see is what you get.
