Adaptec 8805 can't complete creation of RAID1-array: Final 'Next'-button is missing in MSM (!?)

[donse]

This is a real headache:

When creating a RAID1-array with MSM on 8805 (two identical 12TB HDD - one Host [Device 1] w. app. 6TB original data and one Slave [Device 0] wo data), in the final step/window the 'Next'-button is missing (Edge, Chrome and Mozilla alike).

What is the reason for not being able to finish and complete the expansion, why is 'Next' missing for this final step (screenshot attached and sys.info below picture).
Any ideas - help/advice needed please?

Thx.

Win10 sys:
Windows 10 Pro (22H2) Build 19045.3803
MSI MAG x570 Tomahawk WiFi: BIOS LLC. 1.50, 20-01-2021 (SMBIOS Version 2.8), Embedded Controller Version 255.255 UEFI-mode
AMD Ryzen 7 3700X 8-Core Processor 3.60 GHz
RAM 2 x 32GB Corsair Vengeance LPX DDR4-3200 C16 BK
NVIDIA Geforce RTX3060 Ti 8GB
OS SSD on M2_1: Samsung SSD 980 PRO 1TB (free space app. 413GB / PCIe 4.0 x4)
Workspace SSD on M2_2: Samsung SSD 980 PRO 2TB (free space app. 31.7GB / PCIe 4.0 x4)

Model Adaptec ASR8805
Status Optimal
Firmware Version 7.18-0 (33556)
Installed Memory 1024 MB
Mode RAID (Expose RAW)

 

[i386]

Second device has 0mb free space...

 

[donse]

Second device has 0mb free space...

True. And this is a bit strange.
However, supposedly MSM is only looking for non-allocated disk space here, hence it should read '0' (?).

When initially creating the array with Device 1 (as 'Master' of a RAID1 array), there was 63% (app. 7 TB) of free space according to Win10 Disk Management - and there still is: