Please note that the depot archives are only published for every Sculpt OS release (which usually occurs end of April and end of October).
You may have a look at Building the boot image for instructions how to build the 25.11 boot image from pre-built depot archives.
Alternatively, if you prefer to Reproduce the system from source, you need to change the default depot user (“genodelabs”) to yourself, compile the depot archives, and upload these archives to a webserver. Instructions are provided in the linked section of the Sculpt OS documentation.
Please also note that using one of the quarterly Genode releases (or even the current master/main branch) of the Genode repository in order to build a Sculpt OS image must be considered experimental since the Sculpt scenario is not thoroughly tested in the scope of the quarterly framework releases. As mentioned before, Sculpt OS follows its own release cycle.