I am not sure if I have understood your two questions correctly, but I will try to answer them briefly.
1. SSD is recognised as HDD

a) Deactivate AHCI mode
You may have to deactivate the AHCI mode (Advanced Host Controller Interface) in the BIOS - this applies especially to older mainboards.
b) Start the BIOS and set the AHCI mode to "Disabled", "Off" or "Disabled".
c)Install the latest BIOS drivers
d) Make sure you have installed the latest mainboard and BIOS drivers. Maybe the correct drivers for the SSD controller are missing.
You can also look here on this topic:
https://www.giga.de/extra...

2. booting from the second SSD, or both SSDs ?

Samsung Electronics GmbH
Hello,
Please describe this phenomenon to our support colleagues.
To do so, go to our manufacturer's page and click on the support link.
Our colleagues will be happy to help you.
Kind regards from Schwalbach,
Your Samsung Service Team

Yes exactly, first try to check the bios settings and if possible update to the latest version.
and then you might see more.
It is not a problem for me, as you have formulated it. I have understood it.