Collabora internal link option "target in document" seems not to work

Hello everybody, I’ve tried to create an internal link in an excel sheet using the demo.nextcloud.com area. I selected the “link” option and then the “target in document” option, but the system does not allow me to select any “target in document”. At last: the link option doesn’t seem to work. Please, can you give me some hints to solve the issue? Kind Regards. Andrea