Classic Maple refers to the old Graphical User Interface (GUI) of Maple, which uses only 1D Math (hence there are no Clickable Math features) and does not use Java. It is only available with the 32-bit installation of Maple (on Linux, only for Maple 2015 and earlier), so it has limited use of memory, but it is compatible with screen readers.
You can also make the Standard Interface look more like the Classic Worksheet.
If you started with 64-bit Maple, you can still activate 32-bit Maple with the same purchase code. Once you have it installed, Classic Maple can be found here:
C:\Program Files (x86)\Maple 2020\bin.win\cwmaple.exe
If your operating system is 32-bit, you can find Classic Maple here:
C:\Program Files\Maple 2020\bin.win\cwmaple.exe