For an F4-424 with BIOS MADN0101.V05, upgrading from 6.0.0794 to 7.0.0747 usually doesn't need any extra steps.
The problem you're seeing might be because some drives in your storage pool still have TOS 6 boot partitions, which can conflict with TOS 7. Once you manage to boot into TOS 7, you can consider migrating the system to each storage pool drive one by one, and finally back to the drive you intend to use as the system drive. This will overwrite all old boot partitions.
Also, the internal USB drive is still running the TOS 6 boot system. To prepare for any future reset of TOS 7, you may refer to the following guide to reflash it to the TOS 7‑specific version:
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