You cannot type in the data field.
Rather, you select from available custom panels.
Until you have created and saved a custom panel, nothing will show up as an option there.
This is actually a huge improvement. In older versions, you had to type the name of the panel, and if you typed it wrong, nothing showed up but an error message. Now, you basically get a menu of available panels and cannot go wrong.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB