In addition to using custom code and UI libraries to build custom New and Edit forms, there are some simplifications that SharePoint Online offers to consider.
Leverage existing features of SharePoint: SharePoint provides features to customize the appearance and behavior of forms without writing custom code. You can configure it through SharePoint's list settings interface, such as field settings, column types, validation, etc. These settings can affect the default form rendering. This way, you can adjust the form's display and validation rules without writing custom code.
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Use Power Apps: Power Apps is a low-code/no-code platform for creating custom SharePoint forms. You can use Power Apps to build forms that bind directly to SharePoint columns, and customize the form's appearance and behavior as needed. Power Apps provides a rich set of visual design tools and presets that make it easier to create and customize forms without deep coding.
Using SharePoint's default functionality and Power Apps can help simplify the process of building forms and reduce the writing of custom code. These methods provide an easier way to customize forms, especially when the requirements for form appearance and behavior are not too complicated. But if you need a higher degree of customization and flexibility, using custom code and UI libraries is still a more powerful option.