Installer doesn't see SSD on dev/sda

Hi all,
searched the web and the forum but didn’t find a solution.
Yesterday I dowloaded the v20 KDE ISO and put in on an SD-card (somehow misplaced my box with 20 USB sticks in it) and installed various systems with that.

Now I get to a laptop that I upgraded a bit by ripping out the 500GiB HDD0, replacing it with a new 223GiB SSD. It also has a HDD1 (1.3TiB platter disk).

Laptop Medion MD98108 (Akoya E7221), with Intel i3 @2.3GHz, 8GB RAM and disks as stated above.

Installation live media boots fine and in Dolphin I see the disks (not automatically mounted) as well as with lsblk and partition tools etc etc.

First created some GPT setup with space for GRUB & system on SSD (sda) and swap & /home on HDD1 (sdb). Installation media is seen as sdc. This is consistent over various reboots with inst. disk in various USB or Card Reader. Always sda==SSD, sdb==HDD, sdc==live sys on SD-Card

The problem is that the installer doesn’t seem to see the SSD on sda and only offers to install on the HDD.

In the BIOS Fastboot is disabled, the SATA config is set to AHCI (not IDE) and I can find no RST options (as suggested in other threads with SSD not being recognized, but not just by the installer in those cases it would seem).

I’ve repartitioned various times as MBR or GPT, with or without partition for GRUB (all from the live system, that has absolutely NO issue with seeing the disk), rebooted a gazzilion times between changes etc etc … no avail. The installer just won’t offer to install to the SSD (it isn’t even listed as greyed out in the drop down menu).

Any thoughts?

Thanks in advance!

Update: Okay, so I figure I remove the SSD again from the internal SATA bus, connect it to an external USB cable, install it as USB drive and put it back … but no…

Even when connected as external USB lsblk sees it (now as sdb with the HDD as sda) but the installer still only offers the HDD.

There is a difference though: Dolphin now won’t mount the ext4 partition on the SSD, complaining about “dev/sdb2 already mounted or mount point busy”

I seem to remember I saw that on one of the previous test runs with disk inside as SATA too, but only incidentally once or so… gotto go to work now …

Would appreciate any pointers/thoughts …

P.S. One more thought: Before putting the live ISO on an SD-Card I dd’ed the ISO onto this same SSD and used it a couple of times to boot (connected to USB) with other systems. I think that also still worked when I had it internally on SATA. So the system is able to use the disk during startup with no extra configuration. Later I used the KDE partition manager on the live system to set a nwe partition table (GPT, MBR whatever) as described in first post.

One last test before I gotta run: Unplugged the SSD from USB3 port that it was connected to during boot. Plug it into an USB2 port. Now Dolphin will mount it and lsblk gives it as sdd. Installer still won’t see it.