Upgrading from version 11 to version 12.0.2 does not start

I have version 11.0.0.
NextCloud tells me that version 12.0.2 exists.
I go into the administration to start the update and click on Open Update System.
But nothing happens, nothing happens.
The button has no effect.
I am blocked.
I am the administrator.
What can I do ?
Thank you for your help.

Have you tried manual upgrading it??


Does it work when NextCloud is installed at the OVH host ?
I see there are order lines to do, where do they have to be written ?