Hi.
As you are upgrading from PB 12.5, the most important changes you may find are themes (which may affect any standard visual control). You can look the following links as a start:
Specifying application properties - - Users Guide
ApplyTheme - - PowerScript Reference
Themes will affect how menus show as the colors will be based on theme, as shown in following screenshot:
Here the Dark Theme is used.
Another important change we have in later releases (R2 & R3), is the modernization of graph control. This one works without requiring any change (in case of course your application is using graph control or graph datawindows).
Another change has to do with the ability to use a TabbedView in MDI windows. This change also happens with minimal changes to your application (just two setting need to be adjusted: TabbedView and MaximizeAllTabbedSheets properties on your mdi frame).
Finally there is a ribbonbar available, but for this one, I would agree with Chris, you should wait for PB 2025 which will support an easy menu to ribbonbar transformation.
If you want to see how themes work, you can take a look to SalesDemo Example application that ships with PowerBuilder 2022R3. There you may be able to see how easy you can switch theme, and how an application is affected. Another thing to mention is that themes are customizable, that meaning you have a lot of flexibility to create your own themes.
Andreas.