According to MS public information,the only way to map table columns is to use solution explorer (classic designer).

Title:Open solution explorer

 URL:https://learn.microsoft.com/en-us/power-apps/maker/data-platform/map-entity-fields#open-solution-explorer

But according to another public information,classic app, form, and view designers are deprecated.

Title:Classic app, form, and view designers are deprecated

 URL:https://learn.microsoft.com/en-us/power-platform/important-changes-coming#classic-app-form-and-view-designers-are-deprecated

So,I hope that it will be possible to map table columns using modern designer.