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#11
This would be much easier for you, if you just followed instructions.
As was with <Active> tags in <ModifyPartition> for GPT disk, also the <Extend> tags have nothing to in <ModifyPartition>, just making partitioning to fail. In your last answer file, partitions 2 and 3 have this unnecessary, completely wrong setting.
You set the size of the partition or extend it if / when necessary in <CreatePartition>. In <ModifyPartition> you then tell how to format and label that partition. Because size is already known, or instead of size if that partition will be extended to use all remaining space, you do not put the size again in <ModifyPartition>.
You mentioned that you have read my tutorials. Simple instructions for partitioning in answer file, what belongs where can be found in steps 3.11 through 3.18 in this tutorial: Create media for automated unattended install of Windows 10
Kari