The issue was due to a specific driver that was on the disk controller (this was despite – or perhaps because of! – having applied all available Windows and system updates prior to attempting the OS upgrade). The resolution was to go into Device Manager, expand the IDE ATA/ATAPI controllers and ‘update’ the driver for the listed controller (was shown as an Intel controller) to use the standard Windows driver:
Right-click the installed device
Select ‘Update Driver’
Select ‘Browse my computer for drivers’
Select ‘Let me pick from a list…’
Select ‘Standard SATA AHCI Controller’
Click Next and complete the process (reboot if necessary).
Re-run the Windows 11 installation and all should now be well during the setup reboot process (and it may even update the controller driver back to the Intel variant).