I found the reason, just discovered it by hoving the mouse over the button "Paste", it was a total coincidence that I saw it:
"The content int he H5P clipboard is of a lower version (1.0) than what is supported in this context (1.2). If possible try to have the content you want to paste upgraded, copy it again, and try pasting it here".
My conclusion is that migrating from the plugin to the core activity is really a cumbersome and time-consuming task 🙁.
"The content int he H5P clipboard is of a lower version (1.0) than what is supported in this context (1.2). If possible try to have the content you want to paste upgraded, copy it again, and try pasting it here".
My conclusion is that migrating from the plugin to the core activity is really a cumbersome and time-consuming task 🙁.